Life history trait variation within Northwest Atlantic halibut ( - - PowerPoint PPT Presentation

Life history trait variation within Northwest Atlantic halibut (Hippoglossus hippoglossus) stock domain

Nancy L Shackell, K. French, N.den Heyer, DW Brickman, Z.Wang, K. Ransier

Oceanography and Climate Section, Ocean and Ecosystem Sciences Division, Bedford Institute of Oceanography, Fisheries and Oceans, Canada

• Nov. 16th 2017,

10thIFS, Saint Malo, France

3L 5Y

Newfoundland Overseas France

Managed as two separate stocks: Gulf of Saint Lawrence Scotian Shelf & Southern Grand Banks (Newfoundland) since 1988 Both are experiencing a period of high juvenile recruitment

1970 1976 1982 1988 1994 2000 2006 2012 5 10 15 20 25 30

Total Legal Spawning

Year

Biomass, 1000t

2015 Value of Commercial Groundfish Atlantic Canada = $216 Million

Greenland halibut Atlantic halibut Haddock Atlantic Cod Redfish spp. Flatfishes Other

2015 Value of Commercial Groundfish Canada = $362 Million

Greenland halibut Atantic halibut Pacific halibut Flatfishes Redfish spp. Haddock Cod Other

Halibut survey biomass index

3

Some of what we know… Some of the Knowledge Gap

Atlantic halibut research

Migration routes Spawning Areas History of Overfishing Transboundary stock, dichotomous views: Possibility of smaller scale resident populations

Shackell et al. 2016. ICES J Mar Sci Sietz et al. 2016. J. Northw. Atl. Fish. Sci

Nursery Areas

Stock Structure??

Range expansion/secondary role of closed areas

(Nancy Shackell, Nell den Heyer, Kiyomi French/DFO, Canada) Connectivity Current=2000km; Estimated=250km Mature female Residents: 6 km

Winter Migration: <250km

Size of Juvenile Habitat ~ Adult landings

Q: Are the following consistent with current stock unit domain?

Life history trait A: Nope… Next Step: add Spatial Management to Framework Assessment Genetic landscape (in progress)

5 Shackell et al. 2016 ICESJMar, Boudreau et al. 2017 Ecol&Evol French et al. in press. Fish Bull.

Q: Is there spatial variation in Growth and/or Length at Maturity?

Size

Age

Life History tradeoff

• Growth decreases as energy is

allocated to reproduction

• Selection acts on maximizing

reproductive output

• Slow growers make up fecundity diffs

by larger size (from Berrigan and Charnov, 1994)

Commonly observed life history strategy in ectotherms

Grow slower Larger size/age at maturity Grow faster Smaller size/age at maturity

Halibut may exhibit a geographic gradient in length at maturity (Sigourney et al. 2006),

FEMALE LM50%=103cm FEMALE LM50%=119cm

Trumble et al. 1993, Bowering et al 1986

How might life history traits vary across management unit?

Halibut will exhibit slower growth and larger length at maturity in the north grading to faster growth and smaller length at maturity in the south, in response to variability in ambient bottom water temperatures.

Expectations Size

Grow faster Smaller size/age at maturity Grow slower Larger size/age at maturity

Age

Joint Industry DFO/Halibut Longline Survey

• Tagging data to estimate Growth Rate

– Selected all fish that were re-captured in the same NAFO where they were initially tagged and at liberty for >50 days. – Assumed growth followed a von Bertalanffy function and used the least presumptive method

• f Gulland and Holt (1959) for small sample sizes
• Observer data to estimate Length at Maturity

– Logistic regression

Growth Rate

Both males and females grow Fastest in southern area and at same rate elsewhere Predicted annual growth rate for both sexes at 90 cm. Values are marginal means, controlling for length, to account for unbalanced design NORTH SOUTH NORTH SOUTH

Length at Maturity

NORTH SOUTH

At this stage,

• South: growing faster and

maturing at smaller sizes than more northerly regions

• consistent with published

estimates

• BUT—no GRADIENT

FEMALE 103cm FEMALE 119cm

NORTH SOUTH NORTH SOUTH

Temperature Trends

• Most optimal habitat corresponds with warmer waters

Growing degree days (GDD) as is used in agriculture and fish (Neuheimer et

• al. 2008).

GDD =number of days (2001-2015) multiplied by a daily temperature threshold (3°C). GDD was matched to each sample

.

Are Life history traits related to growing conditions?

FISHING HISTORY

• <1700’s-early 1800’s

Halibut=NUISANCE in US Cod fishery (not easy to salt)

19

http://www.photolib.noaa.gov/700s/figb0010.jpg

Commercial

fresh fish on ice

1836L overfished By 1850 L overfished

…not so heavily fished

1880= L Collapse

• Head to Canada

under Treaty of Paris (1783) By 1850 L overfished US fishermen predominate. Canadians not in until 1900s Train system improves in early 1800s providing easier access to Ice PS Longlines select larger fish

• Common tradeoff of growth and size at

maturity is reflected in our results.

• Fast growth and smaller length at maturity

were estimated from separate individuals all sampled within division 4X (and the contrary in northerly divisions)

• Division estimates of growth and length at

maturity are comparable to literature: (Trumble et al 1993, Sigourney et al 2006, Armsworthy and Campana, 2010, Beaty and Chen 2017)

• Working hypothesis (until more data

accrues): 4X is different from all other northerly regions. Our combined work suggests: 2-3 substocks, where one area is currently being “subsidized/rescued” by another.

Summary

• Thank you/Merci!

Length at Maturity (LM50%)

c

Fit logistic regressions to estimate L50%

Canadian and Foreign Landings

South and West Newfoundland Scotian Shelf & Gulf of St. Lawrence

Some of this Greenland halibut

24

Connectivity

• Coherent temporal patterns
• n average 250km

(smaller than current domain ~2000km) Persistent areas But …those in sNF disappeared

Adapted from http://www.iiasa.ac.at/web/scientificUpdate/2013/researchProgram/EvolutionandEcology/EvolutionaryConsumption.html

Unit Stock

…all of this affects all of that->

Fully saturated generalized linear model, ~average (Length at Recapture and Length at Release), NAFO and Sex as factors

Fishing Before and After Moratorium

Landings of cod, halibut and other groundfish have decreased dramatically since the cod moratorium (1992-1994)

ASSUMPTION: One Stock from southern Grand Banks to 40°N in USA (~2000km) Initial investigation had climate change focus—highly relevant in warming waters.

Halibut from 1965-2013

WHY?—Climate change? too hot in US? Work work work => (no)