Nearshore fish communities response to habitat variability

1
Nearshore fish communities response to habitat
variability
Terril P. Efird School of Fisheries and Ocean
Sciences University of Alaska Fairbanks
2
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

3
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

4
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

5
Size distribution of Pacific Cod, Gadus
macrocephalus, in kelp forests of Kachemak Bay,
Alaska
6
Background Pacific Cod

• Domestic longline, trawl, and pot fishery
  (Thompson Dorn 2005)
• 150 million/year (ADFG 2008)
• Structure communities (Livingston 1989)
• Trophic link to SSL (Merrick 1997)

7
Background Pacific Cod

• Intertidal shallow subtidal as juveniles
• Oceanic as adults
• Use kelp forest during transition
• Predator refuge
• Foraging
• High relative abundance

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Background Kelp Forests

• Heterogeneous
• Size
• Understory abundance
• Rugosity

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Background Kelp Forests

• Temporal variability
• Annual species
• (OClair Linstrom 2000)
• Kelp forest shrinking
• (Estes et al 2004)
• Forest forming species shift
• (Dames Moore 1976)

10
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.

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Methods

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

500 m
South Yukon
Outside Hesketh
Sauna
Inside Hesketh
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Fish Surveys
Bodkin 1988

• Visual Transects
• 30mx2mx2m
• Benthic midwater
• All G. macrocephalus counted and sized

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Benthic Habitat Surveys
Bodkin 1988

• Data collected on benthic line
• Understory abundance est. with ¼ m quads
• Rugosity measures taken with PVC bar and chain

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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

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Results Forest Size
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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.

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Results Understory Abundance
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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.

19
Results Rugosity
20
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

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Results Rugosity
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Conclusions

• Bigger fish were found in bigger forests
• Smaller fish were found in areas with greater
  cover
• Rugosity?

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Whats next?

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

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Whats next?

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

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Thank You

• Funding
• Rasmuson Fisheries Research Center
• Advisor
• Dr. Brenda Konar
• Logistics
• Nathan Stewart and Patrick Lane
• Hans and Leila Pederson
• Institutional Support

26
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.