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

Amended from: Hare, Steven. Changes in mean weight at age for female Pacific halibut in Alaska, 1925-2000.

7 8 9 10 11 12 13 14 15 16 17 18

Age (years) Mean Weight (pounds)

140 120 100 80 60 40 20

1920-39 1940-59 1960-69 1970-79 1980-89 1990-99 2000-2016

Changes in abundance Size selective fishing mortality Changes in diet

Clark and Hare 2002; IPHC 2013, Gaichas et al 2011; Sullivan 2016 IPHC 2011; IPHC 2013; Gaichas et al 2011 Conover and Munch 2002, Stephen et al. 2011, IPHC 2013; Sullivan 2016

Photo: North Country Charters

Changes in climate

Clark and Hare 2002; IPHC 2013, Sullivan 2016

d13C d15N d13C d15N

Age

Trophic Level Benthic Pelagic

Fish of size x

Proportion of Diet Posterior Distribution 0.0 0.5 1.0 Fast Growers Proportion of Diet Posterior Distribution 0.0 0.5 1.0 Slow Growers

Slow Fast

Fieldwork

20 40 60 80 100 120 5 10 15 20 25 30

Length (cm) Age (Years)

Males

50 100 150 200 250 5 10 15 20 25 30

Length (cm) Age (Years)

Females

Trophic Level Benthic Pelagic

• 19.0
• 18.0
• 17.0
• 16.0
• 15.0

14.0 15.0 16.0 17.0 18.0 4 6 8 10 12 14 16 18 20 δ13C δ15N Age (years) Slow Growth Fast Growth 80-89 cm female halibut

8 year old female halibut

Benthic Pelagic Trophic Level

Amphipods

Slow growth (Age 11 – 17) Fast growth (Age 6 – 8)

80-89 cm female halibut

Medium growth (Age 9 – 10)

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

Conclusions, Current Projects, and Limitations

Acknowledgements

Fast Lab Technicians Tom and Linda Harris

Questions?

IPHC 1986, 2000, 2008, Orlov and Moukhametov 2007, Roseneau and Byrd 2000

Video from: 7tAkAndy

Results: Female Length-at-Age

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

Results: Male Length-at-Age

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

Sulfur Results: Prey

mean ± standard error

Fish Crab Octopus 15.0 16.0 17.0 18.0 δ34S (‰) Prey Type

Sulfur Results: Prey

mean ± standard error

Fast Slow 14.5 15.0 15.5 16.0 δ34S (‰) Growth Speed

Sulfur Results: Mixing Models

• Crabs

Fishes Octopuses

14 15 16 17 18 14 15 16 17

d34S (%) d15N (%)

• Fast

Slow

• Crabs

Fishes Octopuses

14 15 16 17 18 −20 −18 −16 −14

d13C (%) d15N (%)

• Fast

Slow

0.00 0.25 0.50 0.75 1.00 0.00 0.25 0.50 0.75 1.00

Proportion of Diet Scaled Posterior Density

Crabs Fishes Octopuses

Fast

0.00 0.25 0.50 0.75 1.00 0.00 0.25 0.50 0.75 1.00

Proportion of Diet Scaled Posterior Density

Crabs Fishes Octopuses

Slow

Results: Halibut Diet

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• Crabs

Fishes Octopuses RedThings

12 15 18 21 24 −18 −16 −14

d13C (%) d15N (%)

• Female

Male Unidentified

Amphipods

Crabs

d13C d15N

Crab mean

Fishes and Octopuses

d13C d15N

Results: Age agreement

• 55.7 % age agreement
• 83.5 % ± 1 year

Results: 70 cm male diet

Sex

Size

Location

Year