an analysis of by-catch in the icelandic blue whiting fishery o´ lafur k. pa´lsson curriculum:981...
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An analysis of by-catch in the Icelandic blue whiting fisheryO´ lafur K. Pa´lsson
Curriculum : 981 Seminar
Name : Yun-Ching Chang
School No. : M98310015
Date :
2009/12/7
Marine Research Institute, P.O. Box 1390, 121 Reykjav´ık, Iceland
Received 28 June 2004; received in revised form 14 December 2004; accepted 18 December 2004
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Introduction - Blue whiting (Micromesistius poutassou)
Actinopterygii Gadiformes Gadidae
Classification: Biological features:
Spawning grounds
Feeding grounds
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Total international catch of blue whiting (Micromesistius pautassou) 1973-2003, international catch by selected ICES area 1973-2002, and total Icelandic catch 1973-2003.
Source: ICES fisheries statistics 1973-2001
ICES Fishing area
Feeding ground
Spawning ground
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Fishing Gear: Mid-water trawls of Iceland
Gloria mid-water trawls Fishing grounds of blue whiting in Iceland
Iceland
It operates without touching the bottom and is frequently
trawled at depths of a few hundred metres in the redfish fi
shery, where the minimum mesh size in the cod end is 13
5-155 mm, depending on fishing area. The meshes get inc
reasingly larger as they are closer to the opening, where t
hey are commonly 64 metres. The opening of the net ca
n be up to 23,000 m2, the size of 5 football fields.
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Characters of blue whiting fishery in Iceland
The Icelandic blue whiting fishery is a highly modernized one, capable of
locating, catching and landing large amounts of fish within a short period of
time.
Hidden mortality in fisheries may appear in many different forms, such as
accidental by-catch in a given fishery. In recent years, concerns have been raised
as to the potential by-catch in modern pelagic trawl fisheries and its effect on the
fish stocks subjected to the by-catch.
Why do this research? Reasons and Goals ?
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The alternative possibility is to sample the catch during landing. This approach
enables relatively easy access to the catch, and a convenient setup for the
subsequent handling of the samples for specific measurements.
Materials and methods – Sampling sites
Sampling sites of Iceland Trips for sampling were planned to be
selected randomly from the operating
fleet, consisting of 21 vessels.
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From the first 1,000 t of a catch, one sample was taken per 100 t, on average. From t
he part of a catch in excess of 1,000 t one sample was taken per 200 t on average, or
a maximum of five samples.
Materials and methods – Number of samples
The total weight of the sample was measured. The planned weight of a sample was
approximately 500 kg, but most samples were 400–600 kg.
By-catch rate (%) was calculated as weight
of by-catch species per 100 kg of catch. Si
mple t-test was used to calculate confidence
intervals.
Fishing boat of mid-water trawl in Iceland
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Blue whiting catch and effort of the Icelandic fleet, and sampling intensity in the by-catch programme by months 2003, showing sampling operations (lines 1–3) and operations of the fleet (lines 4–6)
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Results
Frequency and quantity
Spatial and seasonal distribution
Length distribution
By-catch analysis
1.
2.
3.
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Frequency distribution of by-catch by numbers in samples in the Icelandic blue whiting fishery 2003
Cycloperus lumpus
Pollachius virens Argentina silus
Gadus morhua
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Results of by-catch analysis, showing sample level figures, by-catch values by weight and numbers raised to total catch weight, and by-catch rate (% weight)
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Variability in by-catch among and within trips, using ANOVA with fish numbers per trip as response and trip as factor
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Topographic chart around Iceland and
Faroese waters
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Geographic positions of sampled hauls and all hauls of the Icelandic blue whiting fleet 2003
March - April May June
July August September - December
Source: log-book database of the Marine Research Institute
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Spatial distribution of saithe (Pollachius virens) by-catch rates (%) in hauls of sampled trips 2003
May - June July
August September - November
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Spatial distribution of silver smelt (Argentina silus) by-catch rates (%) in hauls of sampled trips 2003
May - June July
August September - November
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Spatial distribution of cod (Gadus morhua) by-catch rates (%) in hauls of sampled trips 2003
May - June July
August September - November
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Spatial distribution of lumpsucker (Cyclopterus lumpus) by-catch rates (%) in hauls of sampled trips 2003
May - June July
August September - November
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Division of by-catch in the Icelandic blue whiting fishery between the EEZs of Iceland and Faroes
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Length distributions (numbers) of by-catch species in the Icelandic blue whiting fishery 2003
Pollachius virens
Gadus morhua
Sebastes marinus
Argentina silus
Cycloperus lumpus
Sebastes mentella
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Discussion – By-catch rate, frequency and distribution
The highest frequency of by-catch was observed for saithe and silver smelt, for whi
ch 21.1% and 19.1% of the samples, respectively, were positive. For other species t
he frequency of by-catch was less than 6%.
It should be noted that the EEZ split of by-cat
ches is hardly more than an approximation to
a real spatial separation of the stocks.
Relationships between by-catches and catches.
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The most feasible way to reduce the by-catch is to mount size selective sorting grids
on the trawls that sort larger fish out of the trawl, but retain smaller sized fish as the
target species.
Considering the huge size of the gear used and the great amount of the target species
caught, the frequency and quantity of by-catch appears in fact rather low.
Discussion – Fishing gear for reducing the by-catch
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Thanks for your attention !