nearshore fish communities response to habitat variability
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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.
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