Nearshore fish communities response to habitat variability

Terril P. Efird

School of Fisheries and Ocean Sciences

University of Alaska Fairbanks

Spatial distribution

• Fish spatially distribute based on habitat preference

• Within a given habitat fish composition, size and abundance vary

• Two factors – Kelp forest size – Kelp composition

Thesis

Objectives:• Determine how fish

communities vary with kelp forest size

• Determine how fish communities vary with variation in kelp species composition

Parameters measured:• Fish composition and

density• Fish total length (TL)• Kelp species composition

and density • Kelp forest size

Thesis progress

• Summer 2008– Field work

• Proof of concept • Proof of methods

• Fall 2008– Data Analysis

• Winter 2009– Presented as a poster at the

Kachemak Bay Science Conference

Size distribution of Pacific Cod, Gadus macrocephalus, in kelp

forests of Kachemak Bay, Alaska

• Domestic longline, trawl, and pot fishery (Thompson & Dorn 2005)

• $150 million/year (ADFG 2008)

• Structure communities (Livingston 1989)

• Trophic link to SSL (Merrick 1997)

Background: Pacific Cod

Background: Pacific Cod

• Intertidal & shallow subtidal as juveniles

• Oceanic as adults• Use kelp forest during

transition– Predator refuge– Foraging

• High relative abundance

Background: Kelp Forests

• Heterogeneous – Size – Understory abundance– Rugosity

Background: Kelp Forests

• Temporal variability– Annual species

(O’Clair & Linstrom 2000)

– Kelp forest shrinking

(Estes et al 2004)– Forest forming species

shift

(Dames & Moore 1976)

Objective and Hypotheses

• Objective– To determine how G. macrocephalus stratify spatially

throughout kelp habitats based on fish total length (TL) and habitat characteristics.

• Hypotheses– G. macrocephalus TL will positively correlate with

increasing kelp forest size.– G. macrocephalus TL will negatively correlate with

increasing understory abundance.– G. macrocephalus TL will negatively correlate with

increasing habitat rugosity.

Methods• Southern Kachemak Bay• Four sites• Fish and habitat surveys• 3 surveys per site

Outside Hesketh

Inside Hesketh

Sauna

South Yukon

500 m

Fish Surveys

• Visual Transects– 30mx2mx2m

• Benthic & midwater• All G. macrocephalus counted

and sized

Bodkin 1988

Benthic Habitat Surveys

• Data collected on benthic line

• Understory abundance est. with ¼ m quads

• Rugosity measures taken with PVC bar and chain

Bodkin 1988

Surface Habitat Surveys

• Forest size was measured at slack low tide

• A small boat traced the outline of the forest canopy

• GPS track lines were then downloaded and the area calculated

Results: Forest Size

0 5000 10000 15000 20000 250000

5

10

15

20

25

30R² = 0.718557557060375

Kelp Forest Size (m2)

Avg Fish TL (cm)

Results

• Hypotheses– G. macrocephalus TL will positively correlate with

increase in kelp forest size. – G. macrocephalus TL will negatively correlate with

increase in understory abundance.– G. macrocephalus TL will negatively correlate with

increase in habitat rugosity.

Results: Understory Abundance

0 2 4 6 8 10 12 14 16 180

5

10

15

20

25

30

R² = 0.950420557061451

Understory Algal Abundance (Ind/0.25m2)

Avg Fish TL (cm)

Results

• Hypotheses– G. macrocephalus TL will positively correlate with

increase in kelp forest size. – G. macrocephalus TL will negatively correlate with

increase in understory abundance. – G. macrocephalus TL will negatively correlate with

increase in habitat rugosity.

Results: Rugosity

0 5 10 15 20 25 30 35 40 450

5

10

15

20

25

30

R² = 0.929964126345188

Average Site Rugosity (cm)

Avg Fish TL (cm)

Results

• Hypotheses– G. macrocephalus TL will positively correlate with

increase in kelp forest size. – G. macrocephalus TL will negatively correlate with

increase in understory abundance. – G. macrocephalus TL will negatively correlate with

increase in habitat rugosity. No but…

Results: Rugosity

Sauna Inside Hesketh South Yukon Outside Hesketh

0

1

2

3

4

5

6

Increasing Rugosity→

Avg Abundance (fish/m2)

Conclusions

• Bigger fish were found in bigger forests

• Smaller fish were found in areas with greater cover

• Rugosity?

What’s next?

• Kachemak Bay– July 2009– All fish species– 20 sites–Wide range of forest

sizes

What’s next?

• Aleutian Islands– June 2009 & 2010– All fish species– Address generality– 2 kelp species

Near Islands

Rat Islands Andreanof

Islands

Island of Four Mountains

Fox Islands

Alaska

Pacific Ocean

Bering Sea

Aleutian Islands

Thank You

• Funding• Rasmuson Fisheries Research

Center

• Advisor• Dr. Brenda Konar

• Logistics• Nathan Stewart and Patrick

Lane • Hans and Leila Pederson

• Institutional Support

Questions?

References:

Alaska Department of Fish and Game. 2008. Pacific Cod fisheries in Alaska. http://www.cf.adfg.state.ak.us/geninfo/finfish/grndfish/pcod/pcodhome.php

 

Livingston PA. 1989. Interannual trends in Pacific Cod, Gadus macrocephalus, predation on three commercially important crab species in the eastern Bering Sea. Fishery Bulletin. Vol 87(4): 807-827

 

Merrick RL, MK Chumbley and GV Byrd. 1997. Diet diversity of Steller sea lions (Eumetopias jubatus) and their population decline in Alaska: a potential relationship. Canadian Journal of Fisheries and Aquatic Sciences. 54: 1342-1348

Thompson GG and MW Dorn. 2005. Assessment of the Pacific Cod stock in the Gulf of Alaska. Executive summary, National Marine Fisheries Service, National Oceanographic and Atmospheric Administration.