fishing experiments with an alternative longline bait using surplus fish products

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Fisheries Research, 1-2 ( 1991 ) 43-56 43 Elsevier Science Publishers B.V., Amsterdam Fishing experiments with an alternative longline bait using surplus fish products Svein Lekkeborg ~ Institute of Fishery TechnologyResearch, P.O. Box 1964, N-5024 Bergen, Norway (Accepted 11 January 1991 ) ABSTRACT Lokkeborg, S., 1991. Fishing experiments with an alternative ionglinebait using surplus fish products. Fish. Res., 12: 43-56. An alternative Iongline bait based on minced raw materials as feeding stimulants and nylon bag as reinforcement was tested in fishing trials for torsk (Brosme brosme), ling (Molva molva), cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). Compared with natural bait, minced herring (Clupea harengus) enclosed in a nylon bag gave a higher catch rate for haddock (58%), torsk and ling. For cod, the bait compared poorly with natural bait. The texture of the nylon bag had a negative effect on the catch rate, most pronounced for cod and haddock. The metal clip used to close the bag made the bait larger, and this had a selective effect, catching cod of increased mean length. Adding binder to the bait influenced both bait loss and catch rate. INTRODUCTION Considering that the main bait species represent high-quality resources which could alternatively be used for human consumption, the development of new forms of bait is important. This work has generated increasing interest as rising bait costs, variable availability and introduction of mechanized bait- ing systems have restricted the alternatives for fishermen. Until recently, development of artificial bait has concentrated on incorpo- rating feeding stimulants (synthetic chemicals or liquid extracts) into syn- thetic polymers (e.g. Kobayashi, 1975; Mackie et al., 1980; Yamaguchi et al., 1983; Lokkeborg, 1990a). Despite many investigations having been carried out to identify the chemical nature of attractants and feeding stimulants for fish and crustaceans (e.g. Mackie, 1973; Adron and Mackie, 1978; Hidaka et al., 1978; Carr, 1982; Ellingsen and Doving, 1986), only limited success has been attained in applying this knowledge to produce artificial baits. ~Present address: Institute of Marine Research, Department of Marine Resources, Fish Capture Divison, P.O. Box 1964, N-5024 Bergen, Norway. 0165-7836/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.

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Page 1: Fishing experiments with an alternative longline bait using surplus fish products

Fisheries Research, 1-2 ( 1991 ) 43-56 43 Elsevier Science Publishers B.V., Amsterdam

Fishing experiments with an alternative longline bait using surplus fish products

Svein Lekkeborg ~ Institute of Fishery Technology Research, P.O. Box 1964, N-5024 Bergen, Norway

(Accepted 11 January 1991 )

ABSTRACT

Lokkeborg, S., 1991. Fishing experiments with an alternative iongline bait using surplus fish products. Fish. Res., 12: 43-56.

An alternative Iongline bait based on minced raw materials as feeding stimulants and nylon bag as reinforcement was tested in fishing trials for torsk (Brosme brosme), ling (Molva molva), cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). Compared with natural bait, minced herring (Clupea harengus) enclosed in a nylon bag gave a higher catch rate for haddock (58%), torsk and ling. For cod, the bait compared poorly with natural bait. The texture of the nylon bag had a negative effect on the catch rate, most pronounced for cod and haddock. The metal clip used to close the bag made the bait larger, and this had a selective effect, catching cod of increased mean length. Adding binder to the bait influenced both bait loss and catch rate.

INTRODUCTION

Considering that the main bait species represent high-quality resources which could alternatively be used for human consumption, the development of new forms of bait is important. This work has generated increasing interest as rising bait costs, variable availability and introduction of mechanized bait- ing systems have restricted the alternatives for fishermen.

Until recently, development of artificial bait has concentrated on incorpo- rating feeding stimulants (synthetic chemicals or liquid extracts) into syn- thetic polymers (e.g. Kobayashi, 1975; Mackie et al., 1980; Yamaguchi et al., 1983; Lokkeborg, 1990a). Despite many investigations having been carried out to identify the chemical nature of attractants and feeding stimulants for fish and crustaceans (e.g. Mackie, 1973; Adron and Mackie, 1978; Hidaka et al., 1978; Carr, 1982; Ellingsen and Doving, 1986), only limited success has been attained in applying this knowledge to produce artificial baits.

~Present address: Institute of Marine Research, Department of Marine Resources, Fish Capture Divison, P.O. Box 1964, N-5024 Bergen, Norway.

0165-7836/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.

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44 s. LOKKEBORG

The presents paper describes a new approach to this problem, using minced surplus products from the fishing industry as inexpensive stimulants for an alternative longline bait. A bag made of fine-meshed nylon fabric and closed with metal clips was used to reinforce the bait. As some fishes use texture to elicit food intake (Bardach and Villars, 1974; Atema, 1980), possible nega- tive effects on the catching efficiency caused by the nylon bag or the metal clip, were tested. The potential of the nylon bag to reduce bait loss, and of different binders to reduce leaching of minced materials from the bag, were also investigated. Finally, as the herring (Clupea harengus) stocks are now recovering (Anonymous, 1989), the potential of minced herring as feeding stimulant for the bait was tested. Herring was the dominant bait species in the Norwegian longline fishery until these stocks declined (Bjordal, 1984 ).

Torsk ( Brosme brosme ), ling ( Molva molva ), cod ( Gadus morhua ) and haddock (Melanogrammus aeglefinus) are the main species in the Norwe- gian longline fishery, representing 90% of the total landings. The behaviour of cod and haddock towards baited hooks is significantly different (Lokkeborg et al., 1989), and results obtained in fishing trials with different bait types and sizes also indicate a species difference in hooking behaviour between torsk and ling (Bjordal, 1983a,b). Testing was therefore conducted both in the fish- ery for cod and haddock, and in the fishery for torsk and ling.

MATERIALS A N D M E T H O D S

Fishing ground and gear

Trial A was carried out in September 1986 in the fishery for torsk and ling at the coastal banks offAlesund (western Norway) at a depth of 150-255 m, and Trial B in November 1986 in the fishery for cod and haddock off the coast of Finnmark (northern Norway) at a depth of 220-280 m. Both trials were conducted on commercial longliners operating with bottom longlines (Table 1 ).

Experimental design and data recording

To test if the nylon bag or the metal clip negatively affect the catching effi- ciency of the bait, the following experiments were conducted.

Experiment 1: natural bait in a nylon bag not closed at the ends (Fig. 1 (a) ) was compared with natural bait without the nylon bag.

Experiment 2: natural bait in a nylon bag closed at each end by a metal clip (Fig. l (b) ) was compared with natural bait in a nylon bag not closed at the ends (Fig. 1 (a)) .

The bag was made of fine-meshed nylon fabric (Type 40/60; Janka Tekstil A/S, Orsta, Norway), and the clip was made of aluminium (Tipper clip;

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ALTERNATIVE LONGL1NE BAIT USING SURPLUS FISH PRODUCTS 45

TABLE 1

Gear parameters for longlines used in the fishery for torsk and ling (Trial A), and the fishery for cod and haddock (Trial B)

Trial A Trial B

Mainline Material Spun polyester Polyamide, multifil. Diameter (mm) 7 4.8

Snood Material Polyester Polyamide, monofil. Diameter (mm) 1.2 0.8 Length (cm) 50 55 Mounting Knotted Swivel

Hook Type Mustad Kirby Sea O'Shaugnessy Quality 7330 34184 Size No. 6 No. 4/0 Spacing (cm) 185 160

Soak time (h) 3-10 7-28 Bait

Type Mackerel; squid Squid Size (g) 45.6, 58.2 19.8

Icm

a b c

Fig. 1. Different types of baits tested: (a) squid bait in a nylon bag; (b) squid bait in a nylon bag closed with clips; (c) nylon bag containing minced raw materials.

H. J a n s o n A / S , Bergen, N o r w a y ) . E x p e r i m e n t 1 was c a r d e d out in b o t h trials, whe rea s E x p e r i m e n t 2 was ca r r i ed ou t on ly in Tr i a l B.

T h e p o t e n t i a l o f t w o d i f f e ren t b i nde r s to r educe leaching o f m i n c e d m a t e - r ials f r o m the bag was t e s t ed in Tr i a l A by c o m p a r i n g the ca t ch ing e f f ic iency

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46 S. LOKKEBORG

of mackerel (Scomber scombrus) bait with that of a nylon bag containing minced mackerel and the following binders.

Experiment 3: guar gum, 2% (Guarmehl 5856; Protan A/S, Drammen, Norway). This concentration was chosen on the basis of previous findings (Lokkeborg, 1986).

Experiment 4: gelatin, 50% (prepared from collagen offish skin by Nils H. Nilsen A/S, BAtsfjord, Norway). This concentration was recommended by the producer.

Herring was tested as a feeding stimulant for the bait in both trials by com- paring the catching efficiency of natural bait with that of the following.

Experiment 5: nylon bag containing minced herring and guar gum, 2% in Trial A and 4% in Trial B. A higher concentration was used in Trial B because of the longer soak time in this trial (see Table 1 ).

A total of 1100-3300 hooks were set in each experiment. The two baits to be compared were each baited in clusters of about 50 similarly baited hooks. Comparisons made in Trial A were primarily based on mackerel as reference bait. The catch rates obtained in Experiments 3 and 4 were, however, very low. Mackerel is normally used in combination with squid (in a 2:1 ratio) in the fishery for torsk and ling, and this combination has been shown to be more effective than mackerel alone (Franco et al., 1987). Therefore, in Ex- periments 1 and 5 in Trial A, every third hook was baited with squid (Illex sp. ) only, both for clusters with reference bait and for those with experimen- tal bait. This may cause an underestimation of the catch difference between reference and experimental bait, but was done to try to increase the total catch, to thereby obtain more data. In the fishery for cod and haddock, squid is usually used as bait, and was therefore used throughout Trial B.

The experimental baits tested in Experiments 3-5 were made by mincing the raw material in a mincer while adding the binder. The minced material was put into a long nylon stocking by a filling machine (used for making sau- sages), the stocking then being cut into sections (bags) and closed at each end by a metal clip (Fig. 1 (c)). The mean weight of 50 experimental baits was 20.8 g for bait tested in Trial A, and 17.0 g for bait tested in Trial B (weights of natural baits are given in Table 1 ). The sizes of experimental and natural baits used in Trial B were similar, whereas experimental baits were smaller than the natural baits used in Trial A, because the fishermen in Trial A normally cut big baits. The hook was attached to the experimental baits by hooking twice through the bag as hooking a mackerel bait through the skin.

During the hauling of the gear, the condition of each hook (species of hooked fish, loss of bait, entanglement, loss of hook), the position of hooking (mouth, swallowed, not observed) and the total length of each fish caught were re- corded on a portable data terminal (Micronic 445; Floen, 1985 ).

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ALTERNATIVE LONGLINE BAIT USING SURPLUS FISH PRODUCTS 47

RESULTS

The effect of the nylon bag

Enclosing natural bait in a nylon bag gave, in comparison with bait without a nylon bag, a higher catch rate for torsk (34%), no difference for ling and lower catch rates for cod and haddock (63 and 21% of that of bait without a nylon bag, respectively; Table 2). The mean lengths of cod and ling were higher for fish caught on bait in a bag than for those on bait without a bag. There were no size differences for torsk and haddock.

The hooking position for torsk indicated that bait in a bag caught more mouth-hooked fish than bait without a bag (Table 3 ). There were no differ-

TABLE2

Numbers and mean lengths of fishes caught on bait in nylon bags (Exp.) and bait without a nylon bag ( Ref. )

Species Bait No. Catch per Mean length 2 type caught 100 hooks ~ (SD)

Torsk Ref. 94 8.9 51.0 (6.4) Exp. 125 11.9" (134%) 51.5 (6.4)

Ling Ref. 41 3.9 87.7 (12.2) Exp. 38 3.6 (94%) 94.1" (14.3)

Cod Ref. 516 34.1 60.9 (7.8) Exp. 299 21.5"** (63%) 62.2* (7.2)

Haddock Ref. 199 13.2 46.1 (6.0) Exp. 39 2.8*** (21%) 46.8 (5.4)

t Values in parentheses are catch of experimental bait given as the percentage of that of reference bait. Differences in catch rate were tested by binomial test: *P< 0.05; **P< 0.01; ***P< 0.001. 2Differences in mean length were tested by two-sample t test: *P< 0.05.

TABLE 3

Hooking positions for fishes caught on bait in nylon bags (Exp.) and bait without a nylon bag (Ref.)

Species Bait Mouth Swallowed Not observed P type (X 2 )

% No. % No. % No.

Torsk Ref. 69.1 65 22.3 21 8.5 8 NS

Exp 80.0 100 14.4 18 5.6 7 Ling Ref. 87.8 36 0.0 0 12.0 5

NS Exp. 78.9 30 0.0 0 21.1 8

Cod Ref. 35.1 181 51.2 264 13.8 71 NS

Exp. 30.1 90 56.9 170 13.0 39 Haddock Ref. 78.4 156 7.5 15 14.1 28

NS Exp. 76.9 30 2.6 1 20.5 8

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48

TABLE 4

Bait status for bait in nylon bags (Exp.) and bait without a nylon bag (Ref.)

S. LOKKEBORG

Trial Bait Intact I Remnant 2 Loss 3 P type ~2)

% No. % No. % No.

A ReK 11.7 106 8.6 78 79.7 722 <0.01

Exp. 17.7 153 34.4 298 47.9 415 B Re£ 51.7 358 4.5 31 43.8 303

<0.001 Exp. 75.9 767 18.9 191 5.2 53

tMore than 25% of the bait left on the hook. 2Less than 25% of the bait left on the hook. 3No bait left on the hook.

TABLE 5

Numbers and mean lengths of fishes caught on bait in open-ended nylon bags (Ref.) and bait in nylon bags closed with clips (Exp.)

Species Bait No. Catch per Mean length 2 type caught 100 hooks t (SD)

Cod Re£ 175 12.4 60.8 (7.9) Exp. 168 12.6 (101%) 62.6* (7.3)

Haddock Re£ 97 6.9 44.6 (4.8) Exp. 63 4.7*(68%) 45.9 (4.7)

1'2See Table 2.

TABLE 6

Hooking positions for fishes caught on bait in open-ended nylon bags (Ref.) and bait in nylon bags closed with clips (Exp.)

Species Bait Mouth Swallowed Notobserved P type (X 2)

% No. % No. % No.

Cod Ref. 33.7 59 52.6 92 13.7 24 NS

Exp. 36.9 62 53.6 90 9.5 16 Haddock Ref. 77.3 75 5.2 5 17.5 17

NS Exp. 84.1 53 3.2 2 12.7 8

ences for the other species. Bait loss was lower for bait in a bag than for bait without a bag, and considerably higher in the fishery for torsk and ling than in the fishery for cod and haddock, despite a shorter soaking time in the for- mer (Table 4).

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ALTERNATIVE LONGLINE BAIT USING SURPLUS FISH PRODUCTS

The effect of the clip

49

The clips appended to the nylon bag resulted in a lower catch rate for had- dock than that of the same baiting without clips (Table 5 ). For cod there was no such difference in the catch rate, but bait with clips caught cod of greater mean length. The hooking positions for both cod and haddock were similar for the two baits (Table 6). The rate of bait loss was lower for bait with clips than for bait without clips (Table 7 ).

TABLE 7

Bait status for bait in open-ended nylon bags (Ref.) and bait in nylon bags closed with clips ( Exp. )

Bait Intact ~ Remnant 2 L o s s 3 P type (Z 2)

% No. % No. % No.

Ref. 76.3 838 19.8 218 3.9 43 <0.001 Exp. 94.6 1014 3.1 33 2.3 25

L'2'SSee Table 4.

TABLE 8

Numbers and mean lengths of fishes caught on mackerel bait (Nat.) and bag-enclosed bait of minced mackerel and 2% guar gum (Exp.)

Species Bait No. Catch per Mean length 2 type caught 100 hooks ~ (SD)

Torsk Nat. 62 8.1 54.3 (6.2) Exp. 53 7.1 (87%) 52.2 (5.3)

Ling Nat. 10 1.3 85.6 (9.2) Exp. 7 0.9 (71%) 90.1 (15.8)

~'2See Table 2.

TABLE 9

Hooking positions for fishes caught on mackerel bait (Nat.) and bag-enclosed bait of minced mack- erel and 2% guar gum (Exp.)

Species Bait Mouth Swallowed Notobserved P type (g 2 )

% No. % No. % No.

Torsk Nat. 48.4 30 46.8 29 4.8 3 NS Exp. 50.9 27 39.6 21 9.4 5

Ling Nat. 90.0 9 10.0 1 0.0 0 NS Exp. 85.7 6 14.3 1 0.0 0

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50 s. LOKKEBORG

TABLE 10

Bait status for mackerel bait (Nat.) and bag-enclosed bait of minced mackerel and 2% guar gum ( Exp. )

Bait Intact ~ Remnant 2 Empty 3 L o s s 4 p type (Z 2 )

% No. % No. % No. % No.

Nat. 10.1 69 13.8 94 0.0 0 76.1 518 <0.001 Exp. 3.9 27 1.8 12 65.9 451 28.4 194

~More than 25% of the bait left on the hook. 2Less than 25% of the bait left on the hook. 3Empty bag remaining on the hook. 4No bait left on the hook.

TABLE 11

Numbers and mean lengths of fishes caught on mackerel bait (Nat.) and bag-enclosed bait of minced mackerel and 50% gelatin (Exp.)

Species Bait No. Catch per 100 Mean length 2 type caught hooks~ (SD)

Torsk Nat. 40 7.7 51.9 (8.5) Exp. 19 3.7** (48%) 50.1 (8.9)

Ling Nat. 7 1.4 91.8 (13.7) Exp. 1 0.2 (14%) - ( - )

~'2See Table 2.

TABLE 12

Hooking positions for fishes caught on mackerel bait (Nat .) and bag-enclosed bait of minced mack- erel and 50% gelatin (Exp.)

Species Bait Mouth Swallowed Not observed P type (Z 2)

% No. % No. % No.

Torsk Nat. 35.0 14 40.0 16 25.0 10 NS Exp. 57.9 11 26.3 5 ! 5.8 3

Ling Nat. 100.0 7 0.0 0 0.0 0 Exp. 100.0 1 0.0 0 0.0 0 -

The effect of the binders

The comparison between natural bait and nylon bags containing minced mackerel and guar gum gave no significant differences in catch rates, mean lengths or hooking positions for torsk and ling (Tables 8 and 9 ). Bait loss was higher for bait in a nylon bag than for natural bait (Table 10).

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ALTERNATIVE LONGLINE BAIT USING SURPLUS FISH PRODUCTS 51

TABLE 13

Bait status for mackerel bait (Nat.) and bag-enclosed bait of minced mackerel and 50% gelatin (Exp.)

Bait Intact ~ Remnant 2 Empty 3 Loss 4 P type (X 2 )

% No. % No. % No. % No.

Nat. 6.9 32 4.8 22 0.0 0 88.3 408 <0.001

Exp. 93.5 462 1.2 6 0.0 0 5.3 26

1'2'3"4See Table 10.

TABLE 14

Numbers and mean lengths of fishes caught on natural bait (Nat.) and bag-enclosed bait of minced herring and guar gum (Exp.)

Species Bait No. Catch per 100 Mean length 2 type caught hooks t (SD)

Torsk Nat. 47 3.1 51.8 (6.7) Exp. 59 3.9 (124%) 52.9 (8.7)

Ling Nat. 44 2.9 95.2 (15.9) Exp. 51 3.4 (115%) 97.4 (18.4)

Cod Nat. 352 27.4 62.0 (7.7) Exp. 64 5.1"** (18%) 63.7 (11.6)

Haddock Nat. 173 13.4 47.6 (6.1) Exp. 269 21.3"** (158%) 47.7 (6.3)

1'2See Table 2.

TABLE 15

Hooking positions for fishes caught on natural bait (Nat.) and bag-enclosed bait of minced herring and guar gum (Exp.)

Species Bait Mouth Swallowed Not observed P type (Z 2 )

% No. % No. % No.

Torsk Nat. 40.4 19 48.9 23 10.6 5 NS

Exp. 61.0 36 37.3 22 1.7 1 Ling Nat. 93.2 41 4.5 2 2.3 1

NS Exp. 88.2 45 3.9 2 7.8 4

Cod Nat. 38.4 135 51.7 182 9.9 35 <0.001

Exp. 65.6 42 23.4 15 10.9 7 Haddock Nat. 86.1 149 6.9 12 6.9 12

<0.001 Exp. 93.3 251 0.4 1 6.3 17

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52 s. LOKKEBORG

TABLE 16

Bait status for natural bait (Nat.) and bag-enclosed bait of minced herring and guar gum (Exp.) from trial A (torsk and ling) and trial B (cod and haddock)

Trial Bait Intact ~ Remnant 2 Empty 3 LOSS 4 P type (Z 2)

% No. % No. % No. % No.

A Nat. 40.4 562 4.4 61 0.0 0 55.2 767 <0.01

Exp. 47.5 655 3.8 53 18.0 248 30.7 423 B Nat. 62.3 423 3.7 25 0.0 0 34.0 231

<0.001 Exp. 68.1 557 21.5 176 2.3 0 8.1 66

t,2'3'4See Table 10.

For torsk, a nylon bag with gelatin as binder gave a lower catch rate than natural bait (Table 11 ). There were no significant differences in mean length or hooking position (Table 12). Bait loss was considerably lower for bag- enclosed bait than for natural bait (Table 13 ).

Minced herring as stimulant

Compared with natural bait, bag-enclosed bait of minced herring gave a 58% higher catch rate for haddock, a non-significant catch increase for torsk and ling (24% and 15%, respectively), but a considerably lower catch rate for cod (Table 14). There were no differences in mean fish lengths. The bag- enclosed bait gave lower proportions of cod and haddock that had swallowed the bait (Table 15). The same tendency, though not significant, is seen for torsk. The bag-enclosed bait gave less bait loss than natural bait (Table 16).

DISCUSSION

The effect of the nylon bag

Experiment 1 clearly showed that the nylon bag had a negative effect on the catch rates for cod and haddock. This effect may be explained by a restraint in bait intake and swallowing response caused by the texture of the nylon bag. Some fishes use taste and texture to elicit both pick-up behaviour and inges- tion, thereby sorting food items from less palatable or inedible materials (Atema, 1980). Thus, fish may more often reject a bait when it is covered with a nylon bag. Johannessen (1984) obtained a similar decrease in the catch rate for cod with shrimp bait in a nylon bag.

Bait in a bag gave a more pronounced catch decrease for haddock than for cod, indicating a stronger effect of bait texture on haddock. In addition, this species difference may be due to a difference in hooking behaviour between

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ALTERNATIVE LONGLINE BAIT USING SURPLUS FISH PRODUCTS 5 3

haddock and cod. Because haddock bite at parts of the bait, whereas cod com- pletely ingest the bait, decreasing the bait size could increase the hooking probability for haddock (L~kkeborg et al., 1989). Bait scavengers and fish nibbling at the bait without a bag might have made this bait smaller, thereby increasing the hooking probability. Bait predation could not influence the size of the bait in a bag to the same degree because the bag reduced bait loss (see Table 4). Furthermore, remnants of bait in the bag might still have appeared large to the fish owing to the presence of the bag.

For torsk, the nylon bag caused an increase in the catch rate ( 34% ). It seems unlikely that this could be due to a preference for bait in a bag. A more rea- sonable explanation is the difference in bait loss between the baits. When the gear was hauled, the proportion of intact bait was 50% higher for bait in a bag than for bait without a bag (see Table 4). Some of this loss had already oc- curred upon setting the gear. The number of hooks fishing might therefore have been higher for the bait in a bag during the whole fishing period, result- ing in the observed catch increase for torsk.

In addition, the catch increase for torsk was obtained only for fish hooked in the mouth (see Table 3). A lower proportion of swallowed bait for bag- enclosed bait than for natural bait was also seen in the other experiments. The hooking position therefore indicates that the nylon bag inhibited the swallow- ing response in torsk. Although few ling were caught, the result indicates a negative effect of the nylon bag for ling also, as bag-enclosed bait gave no catch increase in spite of lower bait loss.

Bag-enclosed bait caught cod and ling of higher mean length than bait with- out a bag, indicating that the effect of texture was less pronounced in larger fish. Larger cod have greater experience of food uptake (Palsson, 1981; Mehl et al., 1985) and therefore have greater experience of prey types of different tastes and textures. A lower proportion of small cod in catches taken by arti- ficial bait than by natural bait was also explained by a lesser response of small cod towards artificial bait, this being due to its shape and texture (Lokkeborg, 1990b). In addition, the observed difference in mean length may be due to a difference in bait size caused by the reduced bait loss for the bag-enclosed bait. Larger baits have been shown to catch larger cod than smaller baits (Jo- hannessen, 1983 ). Knowledge about the feeding behaviour of ling is scarce.

The effect of the clip

The result for cod in Experiment 2 showed equal catch rates but higher mean length for bait with clips, demonstrating an effect on size selection but not on catching efficiency. Bait with clips was larger than bait without clips because the bag had to be made longer for the former (see Figs. 1 (a) and 1 (b) ). As larger baits have been shown to catch larger cod than smaller baits

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54 s. LOKKEBORG

(Johannessen, 1983 ), the observed difference in mean cod length is probably due to the difference in total bait size, and not to the clip as such.

Different bait sizes may also explain the lower catch rate of haddock for bait with clips than for bait without. Decreasing the bait size has been shown to considerably increase the catch rate for haddock (Johannessen, 1983 ). The lower catch rate for bait with clips may thus be an effect of larger bait size. A mechanical impact of the clip itself may further reduce the catch of haddock.

The effect of the binders

The use ofguar gum as binder gave a high catch rate and higher proportion of empty bags (66%), whereas nylon bags containing gelatin gave a low catch rate and no empty bags. This shows that the binder influenced both catch rate and the leaching of minced materials from the bag. Decreasing the release rate of feeding attractants from mackerel bait has been shown to decrease the catch rate for torsk (l_~kkeborg, 1989). A binder of high binding power causing a low leaching rate of material from the bag will probably also cause a slow release rate of attractants. Such an effect of the binder may explain the low catch rate for gelatin. Lowering the concentration of this binder may improve the catching efficiency.

Minced herring as stimulant

Bag-enclosed bait of minced herring gave higher catch rates for torsk, ling and haddock than natural bait. The high catch increase for haddock (58%) indicates that feeding stimulants released from herring more than compen- sated for the negative effect of the texture of the nylon bag. This negative effect might also have been reduced when using minced materials which may percolate through the meshes of the bag thereby masking the threads. The low catch rate for cod is probably due to lack of critical attractants and stimulants in herring. This is supported by the low incidence of swallowed hooks. Cod prey on herring (Bergstad et al., 1987; Mehl, 1989), but as vision is the pri- mary sense for midwater feeding (Brawn, 1969), attacks towards fish prey are probably mostly visually stimulated.

The promising results for three of the four main species in Norwegian long- lining achieved with herring as a raw material are interesting considering the present recovery of the herring stocks (Anonymous, 1989). Herring is re- garded as an efficient bait, and was the dominant bait species in the Norwe- gian longline fishery until the decline in the herring stocks (Bjordal, 1984). This resource may prove to be a suitable raw material for a bait based on minced surplus products enclosed within nylon bags. The low catch of cod shows that this bait may be species-selective, and other resources must be tested as potential stimulants for the cod fishery. Natural prey organisms, fish

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ALTERNATIVE LONGLINE BAIT USING SURPLUS FISH PRODUCTS 5 5

processing waste and trash fish could also be used as feeding stimulants for this type of bait.

ACKNOWLEDGEMENTS

I am grateful to the captains and crews of the "Bjornsvik" and the "Nes- bakk" for their helpful cooperation and assistance in the collection of the data. I am also indebted to A. Fern/5 for valuable remarks made on the manuscript, to A. Brettingen for improving the English, and to the Norwegian Fisheries Research Council that supported the study financially.

REFERENCES

Adron, J.W. and Mackie, A.M., 1978. Studies on the chemical nature of feeding stimulants for rainbow trout, Salmo gairdneri Richardson. J. Fish. Biol., 12:303-310.

Anonymous, 1989. Resource survey for 1989 and marine environment report for 1988. Fisken og Havet, Spec. Publ., 1, 99 pp. (in Norwegian). Available from Institute of Marine Re- search, Bergen, Norway.

Atema, J., 1980. Chemical senses, chemical signals and feeding behavior in fishes. In: J.E. Bar- dach, J.J. Magnuson, R.C. May and J.M. Reinhart (Editors), Fish Behavior and Its Use in the Capture and Culture of Fishes. ICLARM Conference Proceedings 5, Manila, pp. 57- I 01.

Bardach, J.E. and Villars, T., 1974. The chemical senses of fishes. In: P.T. Grant and A.M. Mackie (Editors), Chemoreception in Marine Organisms. Academic Press, New York, pp. 49-104.

Bergstad, O.A., Jorgensen, T. and Dragesund, O., 1987. Life history and ecology of the gadoid resources of the Barents Sea. Fish. Res., 5:119-161.

Bjordal, A., 1983a. Effect of different long-line baits (mackerel, squid) on catch rates and selec- tivity for tusk and ling. Count. Meet. Int. Counc. Explor. Sea, B:31,9 pp.

Bjordal, A., 1983b. Full scale trials with new hook designs and reduced size of bait. Counc. Meet. Int. Counc. Explor. Sea, B: 32, 7 pp.

Bjordal, ~,., 1984. Traditional baits used in Norwegian longlining. Int. Counc. Explor. Sea Ad Hoc Working Group on Artificial Bait and Bait Attraction, Hirtshals 1984, 5 pp.

Brawn, V.M., 1969. Feeding behaviour of cod (Gadus morhua). J. Fish. Res. B. Can., 26: 583- 596.

Carr, W.E.S., 1982. Chemical stimulation of feeding behavior. In: T.J. Hara (Editor), Chemo- reception in Fishes. Elsevier, Amsterdam, pp. 259-273.

Ellingsen, O.F. and Doving, K.B., 1986. Chemical fractionation of shrimp extracts inducing bottom food search behavior in cod (Gadus morhua L. ). J. Chem. Ecol., 12:155-168.

Floen, S., 1985. Experimental design for data collection and analysis in comparative Iongline fishing trials. Int. Counc. Explor. Sea Ad Hoc Working Group on Artificial Bait and Bait Attraction, Bergen, 1985, 6 pp,

Franco, J.M., Bjordal, A. and L~kkeborg, S., 1987. Synergistic effects of different baits on the same hook in the longline fishery for hake (Merluccius merluccius) and torsk (Brosme brosrne). Counc. Meet. Int. Counc. Explor. Sea, B:39, 22 pp.

Hidaka, I., Ohsugi, T. and Kubomatsu, T., 1978. Taste receptor stimulation and feeding behav- iour in the puffer, Fugu pardalis. I. Effect of single chemicals. Chem. Senses Flavour, 3:341- 354.

Johannessen, T., 1983. Influence of hook and bait size on catch efficiency and length selection

Page 14: Fishing experiments with an alternative longline bait using surplus fish products

56 s. LOKKEBORG

in longlining for cod (Gadus morhua L.) and haddock (Melanogrammus aeglefinus L.). Cand. real. Thesis, University of Bergen, 109 pp. (in Norwegian).

Johannessen, T., 1984. Fishing experiments with different longline baits for cod, February 1984. Int. Counc. Explor. Sea Ad Hoc Working Group on Artificial Bait and Bait Attraction, Hirt- shals, 1984, 11 pp.

Kobayashi, H., 1975. A study on the success of a fishery with artificial baits for tuna long lines. Bull. Jpn. Soc. Sci. Fish., 41: 175-182.

Lokkeborg, S., 1986. Experiments with alternative longline bait in the fishery for cod; Novem- ber 1985. Rep. Inst. Fish. Tech. Res., Bergen (unpubl.), 45 pp. (in Norwegian).

Lokkeborg, S., 1989. Longline bait: Fish behaviour and the influence of attractant release rate and bait appearance. Dr. Sc. Thesis, University of Bergen, 109 pp.

Lokkeborg, S., 1990a. Rate of release of potential feeding attractants from natural and artificial bait. Fish. Res., 8: 253-261.

Lokkeborg, S., 1990b. Reduced catch of under-sized cod (Gadus morhua) in longlining by using artificial bait. Can. J. Fish. Aquat. Sci., 47:1112-1115.

Lokkeborg, S., Bjordal, A and Fern6, A., 1989. Responses of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) to baited hooks in the natural environment. Can. J. Fish. Aquat. Sci., 46: 1478-1483.

Mackie, A.M., 1973. The chemical basis of food detection in the lobster, Homarus gammarus. Mar. Biol., 21: 103-108.

Mackie, A.M., Grant, P.T., Shelton, R.G.J., Hepper, B.T. and Walne, P.R., 1980. The relative efficiencies of natural and artificial baits for the lobster, Homarus gam marus: laboratory and field trials. J. Cons. Int. Explor. Mer, 39: 123-129.

Mehl, S., 1989. The Northeast Arctic cod stock's consumption of commercially exploited prey species in 1984-1986. Rapp. P.-v. Rrun. Cons. Int. Explor. Mer, 188:185-205.

Mehl, S., Nakken, O., Tjelmeland, S. and Ulltang, O., 1985. The construction of a multi-species model for the Barents Sea with special reference to the cod-capelin interactions. In: M. Alton (Editor), A Workshop on Comparative Biology, Assessment, and Management of Gadoids from the North Pacific and Atlantic Oceans. Proceedings: Part III. Northwest and Alaska Fisheries Center, Seattle, pp. 941-963.

Palsson, O.K., 1981. On the food ofdemersal fish species in Icelandic waters. Coun. Meet. Int. Counc. Explor. Sea, G:25, 46 pp.

Yamaguchi, Y., Nonoda, T., Kobayashi, H., Izawa, K., Jinno, T., Ishikura, I., Uchida, M. and Tonogai, M., 1983. Effectiveness of artificial bait for obtaining higher hooking rate on bot- tom set long-line fishing. Bull. Jpn. Soc. Sci. Fish., 42:1819-1824.