The 2015 stock assessment of Common Snook, Centropomus undecimalis

Transcription

1 The 2015 stock assessment of Common Snook, Centropomus undecimalis Robert Muller, Alexis Trotter, and Philip Stephens 13 January 2016 Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute Orlando, FL

2 Data sources Life History Stock identification Tringali et al. Cold kills Stevens et al. In review Spawning Lowerre-Barbieri et al., Young Age-specific natural mortality Lorenzen Growth, maturity morphometrics, Taylor et al. Fishery Landings and releases MRFSS/MRIP Lengths of fish landed Fish Bio Snook samplers, MRFSS/MRIP and Everglades National Park (), anglers logbooks Lengths of released fish Angler logbooks Ages of landed fish Fish Bio Snook samplers Ages of fish in population FIM samplers Abundance indices FIM, MRFSS, ENP on Environmental factors Red Tide cell counts Temperature FWRI Harmful Algal Bloom program National Buoy Data Center (Venice pier)

3 Stock identification Microsatellite DNA analysis with 24 loci of Florida snook collected from both coasts (total n = 1,396 fish) Tringali et al. () found two highly structured groups with individuals being faithfully assigned to the or stock Loci Reviews in Fisheries Science:116: Fig. 2.2

4 Age - growth FWRI Fishery independent sampling Length is not a good indicator of age Total length (mm) Females Age(yr) Total length (mm) Males N = 2,031 N = 6, Age(yr) Females Males 6 yr old Common Snook Total length (mm) Total length (mm) N = 4,086 N = 7, Age(yr) Age(yr) Fig. 2.6

5 Natural mortality Age-specific natural mortality rates Natural mortality per year Age (yr) The higher natural mortality for the coast reflects more cold kills plus red tides.

6 Maturity Snook are protandrous hermaphrodites (fish hatch as males and then most males transition to females). Spawning occurs in May-September depending upon coast in inlets, on beaches, and nearshore. Because females come from mature males, the sex ratio by age can be used as the female maturity schedule (Taylor et al. ); however, recent acoustic tagging has revealed that snook may remain in the rivers and skip spawning (Trotter et al., Young et al. ). Probability of being female Obs Pred Probability of being female Obs Pred Age (yr) Age (yr) P =e Coast+0.307Age /(1+ e Coast+0.307Age ) where coast = 1 and coast= 0 Fishery Bulletin 98: , Trans Am Fish Soc 141: , MEPS 505:

7 Landings and releases 800,000 Released alive 700,000 Landings Number of fish 600, , , , ,000 On either coast, most of the snook are released. 100, ,500,000 2,000,000 Released alive Landings Note: the vertical axes differ by coast. Number of fish 1,500,000 1,000, , Fig

8 Total harvest Number of snook 160,000 Died subsequent to release 140,000 Landings 120, ,000 80,000 60,000 40,000 20,000 A series of 23 experiments estimated the release mortality rate at 2.13% (Taylor et al. ) Total harvest = Landings % * Releases Number of snook 160, , , ,000 80,000 60,000 40,000 20,000 Died subsequent to release Landings North American Journal of Fisheries Management 21:70-75 Fig

9 Fishing effort 3,000,000 2,500,000 2,000,000 Snook trips 1,500,000 1,000, , Source: National Marine Fisheries Service, Marine Recreational Information Program (MRFSS/MRIP) Fig a

10 Sizes of retained fish Proportion Total length (in) Lengths of snook landed in recent years under minimum size limit (1986-, 24 in one fish greater than 34 in) and two slot limits (-06, in and -, in on the coast and in on the coast) Source: FWRI Snook program and MRFSS/MRIP Proportion Total length (in) Fig

11 Sizes of released fish Proportion <= 12 n = Total length (in) N = 6,233 fish Angler logbooks contain the numbers and the lengths of the fish caught and whether the fish was kept or released. In, the Snook and Gamefish Foundation initiated its Angler Action online program for anglers to provide similar information regarding their trips. The proportions shown here are - average lengths. N = 3,278 fish 0.08 Proportion <= Total length (in)

12 Ages of retained fish n=2,454 - n=2,550 Proportion Ages of snook sampled in recent years under two slot limits (- 05, in and -, in. on the coast and in on the coast) Age (yr) n=4,870 - n= 786 Proportion Age (yr)

13 Ages of released fish Proportion Age (yr) Ages were assigned with year- and coast-specific age-length keys. The first step was to use fishery dependent ages and then age the remaining lengths with fishery independent agelength keys. The figures are - averages Proportion Age (yr)

14 Abundance indices Number per seine haul Number per seine haul Fishery independent monitoring with a 183-m haul seine Fig

15 Abundance indices Number caught per set or interview FIM MRFSS/MRIP There is general agreement among the indices used for guiding the model. All of the indices showed a marked decrease in Number caught per set or interview FIM MRFSS/MRIP ENP Fig.4.1.3

16 Assessment model Snook configuration of Age-Structured Assessment Program Version (ASAP, NMFS Toolbox, Legault and Restrepo ) Recreational fishery Releases were linked to the directed fishery and the release mortality was 2.13% Three abundance indices indices on coast and four indices on the Model is fit to: Landings and releases Abundance indices Age composition of indices, landings, and releases ICCAT WORKING DOCUMENT, SCRS 98/58

17 Benchmarks Transitional spawning potential ratio Assessment assessment Assessment Assessment 40% SPR Transitional spawning potential ratios are calculated using the estimated historical fishing mortality rates and are not in equilibrium. The stock on the coast was very near the 40% objective and the stock on the coast exceeded the objective. tspr F SSB / R SSB / R F F 0 Transitional spawning potential ratio Assesssment Assessment Assessment Assessment 40% SPR Fig

18 Regional comparisons Number of snook per haul seine set 4.00 FIM The two data sources agree. On average the regions with highest and the lowest catch rates were on the coast and the regions on the coast were in between. Bay system MRFSS/MRIP Number per trip Region Fig

19 Regional comparisons Fishery independent haul seine catch rates by region Number of snook per haul seine Tampa Bay Number of snook per haul seine Indian River Number of snook per haul seine Charlotte Harbor Number of snook per haul seine Tequesta Fig

20 Environmental effects Two environmental factors that are known to effect snook are temperature and red tides. Howells and Sonski (1990) found that sub-adult snook ( mm TL) ceased feeding at 14 o C and died at 9 o C. Bennett () estimated the impact of the red tide on snook in Sarasota Bay as part of his thesis. Log Proportion of hours below 14 o 10 (Cells per liter) C Temperature Red tide Northeast Science 11: M.S. Thesis, University of Florida

21 Environmental effects For red tide, we used the age composition from 286 snook otoliths collected by Mote Marine Laboratory personnel on 15 July from Lido Key and New Pass. Lengths were mm TL and ages 2-14 years. Proportion Red Tide For cold kills, we used the age composition from 75 snook otoliths collected by Everglades National Park personnel on 18,19, and 24 January from cold killed snook. Lengths were mm TL and ages 1-10 years. We don t know how many snook die when these events occur. Proportion Cold kill Age (yr) Cold kill Age (yr)

22 Environmental effects Fishing mortality per year (age-7) Recruitment (number of age-1 fish, thousands) ,000 2,500 2,000 1,500 1, Base w/environmental effects w/environmental effects (half) Base Environment Mortality per year (age-7) Spawning biomass (mt) 2.50 Fishing mortality Natural mortality ,600 1,400 1,200 1, Base w/environmental effects w/environmental effects (half) After Fig

23 Environmental effects Spawning biomass (mt) Age-12+ Age-11 Age-10 Age-9 Age-8 Age-7 Age-6 Age-5 Age-4 Age-3 Age-2 Age-1 SSB 40%SPR Spawning biomass by age Note: the spawning biomass on the with the environmental effects shows the truncated age structure after the cold kill. Spawning biomass (mt) 1,600 1,400 1,200 1, Axis Title Age-12+ Age-11 Age-10 Age-9 Age-8 Age-7 Age-6 Age-5 Age-4 Age-3 Age-2 Age-1 SSB 40%SPR

24 Environmental effects Unfished F40%SPR Fished spawning biomass per recruit (kg) Base Enviromental effects Kilograms per recruit 0.40 SSB/R F= SSB/R F Age (yr) tspr SSB/R F=0 F SSB / R SSB / R F F The unfished SSB/R illustrates the impact of the environmental effects. Unfished spawning biomass per recruit (kg) Base Enviromental effects Fig

25 Environmental effects benchmark Base Enviromental effects Transitional spawning potential ratio % SPR Fig

26 Benchmarks F ratio (F gm /F 40%SPR ) F ratio (F gm /F 40%SPR ) SSB ratio (SSB /SSB 40%SPR ) SSB ratio (SSB /SSB 40%SPR ) When the cold kill and the uncertainty in the snook response are considered, the spawning biomass took a severe hit and is recovering. Including environmental effects F ratio (F gm / F 40%SPR ) SSB ratio (SSB / SSB 40%SPR )

27 Questions?