Blue crab ecology and exploitation in a changing climate.

Transcription

1 STAC Workshop 28 March 2017 Blue crab ecology and exploitation in a changing climate. Thomas Miller Chesapeake Biological Laboratory University of Maryland Center for Environmental Science Solomons, MD

2 Global Warming

3 Variability in the Chesapeake Bay Mean ph

4 Blue crab life history

5 Climate and recruitment Recruitment mechanisms poorly understood Recruitment strongly influenced by stock size Role of coastal currents Active behavior Stock recruit modeling suggests roles for June Sept wind stress in lower Bay River discharge (other systems)

6 Growth Growth by molting May molt up to 20 times to reach adult size Characterized by periods of stasis and rapid increases in size, during which the shell is soft Growth per molt Inter-molt period 2 0 5/30/1997 7/19/1997 9/7/ /27/1997

7 C 20 C 24 C Growth per molt Final Size (mm) y = x R² = y = 1.286x R² = y = x R² = Y=1.16x R 2 = Brylawski et al Initial Size (mm) Bilen et al. 2014

8 Intermolt period Intermolt period decreases significantly with temperature Development rate increases with temperature and predicts overwintering at ~10-11 o C IMP increases slightly with size Development rate (/day) IMP (Days) Temperature (oc)( o C)

9 Overall growth Hines et al Temperaturedependent increases in growth decrease time to specific life history events Increases in population productivity expected.

10 Reproduction From Hines et al Period suitable for principal reproductive events increases with temperature Size at maturity tends to decrease with temperature Impacts on fecundity less clear

11 Climate and growth Limiting temperature (~9-11 o C) for growth induces overwinter dormancy. Above limiting temperature, growth well described by stochastic degree-day model Faster growth reduces time to key life history events Data needs: high spatial (<1 km) and temporal (daily) resolution bottom water temperature

12 So what in an acidified estuary?

13 Ocean Acidification CO 2(aq) + H 2 O (l) 11 H 2 CO 3(aq) 22 + H (aq) + HCO 3(aq) 33 + H (aq) 2 + CO 3(aq)

14 Methods: Acidification Growth Experiment

15 No effect of ph on growth

16 Conclusions: pco2 Effects Response Growth per Molt Growth Rate Consumption Gut Energy Content Muscle Energy Content Carapace Thickness Carapace [Ca] Carapace % CaCO3 Carapace [Mg] # pco2 No effect No effect No effect Decrease Decrease Decrease* Increase* Increase* Increase Crab growth was not impacted in more acidic water, but energy storage was decreased. These crabs also had thinner shells but with more [Ca], higher %CaCO3, and more [Mg]. Maintenance of Growth = Less stored energy Less protective shell (?)

17 Climate and acidification For juvenile and adult crabs, acidification likely has little effect on growth Effects of larval stages unknown Potential energetic effect of acidification on ration and on carapace structure, suggesting impacts of acidification on predator-prey interactions. Data needs: Uncertain

18 But what about winter mortality?

19 1 0.8 Females % Survival C, 10ppt 3C, 25ppt 5C, 10ppt 5C, 25ppt Time (days) Males % Survival C, 10ppt 3C, 25ppt 5C, 10ppt 5C, 25ppt Bauer and Miller 2010 Time (days)

20 Survival prediction Survival probability in each cell calculated by inputting the parameter estimates into the survival equation S(t) [ ] λ(β + β Temp+ β Sal β - t λ exp = exp Size) 3 Winter duration Average Temperature Average Salinity

21 Adjusted abundance Baywide Abundance (10 6 ) Original 1200 Adjusted

22 Climate and mortality Strong temperature dependency on mortality Decrease in overwinter mortality with increasing winter temperature Assumed increase in mortality during growing season with temperature Data needs: (i) high resolution winter temperature maps, (ii) prediction of when overwintering will cease (underway), (iii) high resolution temperature fields during growing season

23 Life history patterns Growth seasonal Maturation within 24 months Prolonged exposure to sizedependent cannibalism Temperature-induced winter mortality limitation Growth continuous Maturation within months Size-dependent cannibalism No temperature-induced winter mortality Growth seasonal Maturation within months Moderate exposure to sizedependent cannibalism Temperature-induced winter mortality regulation in cold years Brylawski and Miller 2006 Bauer and Miller 2010 Hines et al. 2010

24 So what are the unknown questions Impacts of climate change on offshore portion of life-cycle largely unknown Impact of climate change on ecosystem components unclear Habitat Predators Is the space for time substitution valid for projections

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27 Environmental gradients Average monthly temperature varies considerably over species range What is the consequence on growth and survival? Average temperature (oc) Savannah, GA Chesapeake Bay Long Island Sound 0 Dec Feb Jan Mar Month

28 Quantifying spatial pattern

29 The Winter Dredge Survey (WDS) Conducted yearly since 1990 Winter crabs are dormant, no movement 1 minute tow of a crab dredge ~1,500 stations per year

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32 Crab distribution maps

33 300 Control rule - adult female abundance 250 Number of crabs (x 10 6 ) Age 1+ females Threshold Target Year

34 Exploitation fractions (age-0+ females) Stock status N=70M Abundance of female age-1+ crabs (millions) U=0.34 U=0.25 N=215 M

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37 Distribution Callinectes is a tropical genera that is widely distributed worldwide. Callinectes sapidus, the blue crab, is distributed from Venezuela, throughout the Caribbean, and up the eastern seaboard to New England.

38 Stochasticity 0.6 Detection of patterns revealed in deterministic projections may be masked by stochasticity. r F

39 Number of crabs (x 10 6 ) Year Age 0 abundance

40 Number of crabs (x 10 6 ) Age 1+ abundance Year

41 Age 1+ female abundance Number of crabs (x 10 6 ) Year

42 Number of crabs (x 10 6 ) Control rule - adult female abundance Age 1+ females Threshold Target Year

43 Female blue crab harvest (x 10 6 ) Maryland Virginia Potomac R MD average VA average PR average Year

44 Fraction females removed Percent of females removed Female-specific target (25.5%) Female-specific threshold (34%) Year

45 2016 Stock status 0.6 N=70M Exploitation fractions (age-0+ females) U=0.34 U= Abundance of female age-1+ crabs (millions) N=215 M