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, Gadusmacrocephalus, 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

8. Background: Kelp Forests • Heterogeneous • Size • Understory abundance • Rugosity

9. 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)

10. Objective and Hypotheses • Objective • To determine how G. macrocephalusstratify spatially throughout kelp habitats based on fish total length (TL) and habitat characteristics. • Hypotheses • G. macrocephalusTL 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.

11. Methods • Southern Kachemak Bay • Four sites • Fish and habitat surveys • 3 surveys per site 500 m South Yukon Outside Hesketh Sauna Inside Hesketh

12. Fish Surveys Bodkin 1988 • Visual Transects • 30mx2mx2m • Benthic & midwater • All G. macrocephalus counted and sized

13. 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

14. 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

15. Results: Forest Size

16. 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.

17. Results: Understory Abundance

18. 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…

21. Results: Rugosity

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

23. What’s next? • Kachemak Bay • July 2009 • All fish species • 20 sites • Wide range of forest sizes

24. Alaska Aleutian Islands Fox Islands Near Islands Bering Sea Island of Four Mountains Rat Islands Andreanof Islands Pacific Ocean What’s next? • Aleutian Islands • June 2009 & 2010 • All fish species • Address generality • 2 kelp species

25. 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, Gadusmacrocephalus, 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 (Eumetopiasjubatus) 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.