Size-at-Age and Diet of Pacific Halibut: Can stable isotopes help - PowerPoint PPT Presentation

Size-at-Age and Diet of Pacific Halibut: Can stable isotopes help explain variability in size-at-age? Sarah Webster, Nathan Wolf, Brad Harris Fisheries, Aquatic Science & Technology Lab - Alaska Pacific University 11 November 2017

Picutre: https://en.wikipedia.org/wiki/Pacific_halibut#/media/File:Pacific_halibut_range.PNG

1970-79 140 1980-89 120 1960-69 Mean Weight (pounds) 100 1940-59 80 1990-99 1920-39 60 2000-2016 40 20 0 7 8 9 10 11 12 13 14 15 16 17 18 Age (years) Amended from: Hare, Steven. Changes in mean weight at age for female Pacific halibut in Alaska, 1925-2000.

Changes in climate Changes in abundance Photo: North Country Charters Clark and Hare 2002; IPHC 2013, Sullivan 2016 Clark and Hare 2002; IPHC 2013, Gaichas et al 2011; Sullivan 2016 Size selective fishing mortality Changes in diet Conover and Munch 2002, Stephen et al. 2011, IPHC 2013; Sullivan 2016 IPHC 2011; IPHC 2013; Gaichas et al 2011

Fish of size x Trophic Level d 13 C d 15 N d 15 N d 13 C Age Benthic Slow Pelagic Fast Fast Growers Slow Growers Posterior Distribution Posterior Distribution 0.0 0.0 0.5 0.5 1.0 1.0 Proportion of Diet Proportion of Diet

Fieldwork

120 Males 100 80 Length (cm) 60 40 20 0 0 5 10 15 20 25 30 Age (Years)

250 Females 200 Length (cm) 150 100 50 0 0 5 10 15 20 25 30 Age (Years)

-15.0 80-89 cm female halibut 18.0 Benthic -16.0 17.0 Trophic Level -17.0 16.0 δ 13 C δ 15 N -18.0 15.0 Pelagic -19.0 14.0 4 6 8 10 12 14 16 18 20 Age (years) Fast Growth Slow Growth

8 year old female halibut

Amphipods Trophic Level Benthic Pelagic

80-89 cm female halibut Slow growth (Age 11 – 17) Medium growth (Age 9 – 10) Fast growth (Age 6 – 8)

Conclusions, Current Projects, and Limitations Faster growing halibut are more enriched in δ15N and δ13C and have more variability in diet than slower growing halibut Developing models to evaluate factors that may contribute to • growth performance Prey library • Discrimination values • Incorporation rates • Spatial differences • Long-term changes in size-at-age and diet • Compound specific isotope analysis •

Acknowledgements Fast Lab Technicians Tom and Linda Harris

Questions?

Video from: 7tAkAndy IPHC 1986, 2000, 2008, Orlov and Moukhametov 2007, Roseneau and Byrd 2000

Results: Female Length-at-Age 100" Female" Male" 90" 80" 70" 60" Number'of'fish' 50" 40" 30" 20" 10" 0" 1" 3" 5" 7" 9" 11" 13" 15" 17" 19" 21" 23" 25" 27" 29" Age'(yrs)'

Results: Male Length-at-Age 100" Female" Male" 90" 80" 70" 60" Number'of'fish' 50" 40" 30" 20" 10" 0" 1" 3" 5" 7" 9" 11" 13" 15" 17" 19" 21" 23" 25" 27" 29" Age'(yrs)'

Sulfur Results: Prey mean ± standard error 18.0 17.0 δ 34 S (‰) 16.0 15.0 Fish Crab Octopus Prey Type

Sulfur Results: Prey mean ± standard error 16.0 15.5 δ 34 S (‰) 15.0 14.5 Fast Slow Growth Speed

Sulfur Results: Mixing Models Fast Fast ● ● ● ● 18 18 Slow Slow ● ● ● ● Octopuses Octopuses ● ● 17 17 ● ● ● ● Fishes Fishes d 15 N (%) d 15 N (%) 16 16 ● ● Crabs Crabs ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 15 15 ● ● ● ● ● ● ● ● ● ● ● ● 14 14 14 15 16 17 − 20 − 18 − 16 − 14 d 34 S (%) d 13 C (%) Fast Slow 1.00 1.00 Crabs Crabs Fishes Fishes Octopuses Octopuses 0.75 0.75 Scaled Posterior Density Scaled Posterior Density 0.50 0.50 0.25 0.25 0.00 0.00 0.00 0.25 0.50 0.75 1.00 0.00 0.25 0.50 0.75 1.00 Proportion of Diet Proportion of Diet

Results: Halibut Diet 24 Amphipods RedThings Female ● Male ● ● Unidentified ● 21 ● ● ● ● d 15 N (%) ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 18 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● Octopuses ● ● ● ● ● ● ● ● Fishes ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● Crabs ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 15 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ●● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 12 − 18 − 16 − 14 d 13 C (%)

Crabs d 15 N Crab mean d 13 C

Fishes and Octopuses d 15 N d 13 C

Results: Age agreement • 55.7 % age agreement • 83.5 % ± 1 year

Results: 70 cm male diet

Sex

Size

Location

Year