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Determining relative selectivity of the gulf menhaden commercial fishery and fishery independent gill net data Southeast Fisheries Science Center Amy M.

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Presentation on theme: "Determining relative selectivity of the gulf menhaden commercial fishery and fishery independent gill net data Southeast Fisheries Science Center Amy M."— Presentation transcript:

1 Determining relative selectivity of the gulf menhaden commercial fishery and fishery independent gill net data Southeast Fisheries Science Center Amy M. Schueller March 11, 2013

2 Summary Gulf menhaden and fishery Fishery independent gill net data What do the gill net length comps look like and how do they inform selectivity? Questions that have arisen since? What next? U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 2

3 Gulf menhaden ( Brevoortia patronus ) and fishery U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 3

4 Gulf menhaden and fishery Clupeid Distributed throughout GoM Concentrated: east TX to FL panhandle Schooling forage fish species U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 4

5 Gulf menhaden and fishery Schools targeted by large, industrial purse seine fishery (reduction) Meal, soluble, oil Assisted by spotter pilots (~70% of sets) Biosamples collected Age Length

6 Gulf menhaden and fishery ~84% of landings in LA, rest in MS Nearshore fishery: 59% harvested 0-3 mi from shore 96% harvested 0-10 mi from shore

7 A ‘Nearshore’ Fishery 2009 Total = 18,352 sets Gulf menhaden and fishery

8 Fishery independent gill net data U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 8

9 Gill net data State of Louisiana Collects samples monthly October-March, twice monthly April-September 2, 2.5, 3, 3.5, and 4 inch stretch mesh Fished as strike nets Samples length of fish captured Structures to provide Gulf menhaden ages are not sampled U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 9

10 Gill net sampling locations U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 10

11 Gill net data Used typical methods to create an index Made a case for ability to accurately provide a picture of the true population fluctuations Same lengths, even broader range than cR Well mixed population (literature) Correlated with cR age-2 catch Used to provide an index of adult abundance to the stock assessment model U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 11

12 What do the length comps look like and how do they inform selectivity? U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 12

13 Selectivity - length comps Because we have no age data available, we need to use the length comps with an age-length key to inform selectivity at age What do the length comps look like compared to the reduction fishery length comps? U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 13

14 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 14 Red = cR Black = LA gill nets

15 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 15 Red = cR Green = LA gill nets

16 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 16 Red = cR Black = LA gill nets

17 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 17

18 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 18

19 Questions that have arisen since? U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 19

20 Questions Is the gill net selectivity dome-shaped or flat-top? Is the cR fishery selectivity dome-shaped or flat- top? What does the cR fishery selectivity look like compared to the gill net selectivity, keeping in mind variability in length by age? If either are dome-shaped, how domed are they? U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 20

21 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 21 Red = cR Black = LA gill nets

22 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 22 Red = cR Black = LA gill nets

23 Questions Are other data available that might help us inform selectivity? Concerned that if dome-shaped selectivity was present that the growth curve would be biased U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 23

24 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 24 L infinity = k = 0.45 t 0 = -0.79

25 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 25 L infinity = k = 0.45 t 0 = -0.79

26 Questions Why doesn’t the growth curve show constant or increased variability in length with age? Selectivity Ageing Sampling U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 26

27 Questions What explanation is there for dome-shaped selectivity to occur? Fishery targeting larger school sizes, which would consist of most abundant schooling age classes (ages 1 and 2) Explored biosamples to relate catch sizes to ages However, catch size is not a function of school size because a set does not always capture an entire school U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 27

28 What next? U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 28

29 What next? (related to earlier questions) Why doesn’t the growth curve show constant or increased variability in length with age? Selectivity Have no way of getting at this Ageing Looking at age comparisons and age increments Simulated ageing error Sampling Ruled out with simulation modeling U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 29

30 What next? What is affected in the stock assessment model? von Bertalanffy curve Weight at age of population Natural mortality Age-length key Fecundity (SSB) – based on mean length at age U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 30

31 What next? Do we see this in other species? Atlantic menhaden Maybe herring? U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 31

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