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
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)
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:116:111-116 Fig. 2.2
Age - growth FWRI Fishery independent sampling Length is not a good indicator of age 0 5 10 15 20 Total length (mm) 0 400 800 1200 Females Age(yr) Total length (mm) 0 400 800 1200 Males N = 2,031 N = 6,727 0 5 10 15 20 Age(yr) Females Males 6 yr old Common Snook Total length (mm) 0 400 800 1200 Total length (mm) 0 400 800 1200 N = 4,086 N = 7,306 0 5 10 15 20 Age(yr) 0 5 10 15 20 Age(yr) Fig. 2.6
Natural mortality Age-specific natural mortality rates Natural mortality per year 0.60 0.40 0.30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20+ Age (yr) The higher natural mortality for the coast reflects more cold kills plus red tides.
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 0.80 0.60 0.40 Obs Pred Probability of being female 0.80 0.60 0.40 Obs Pred 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Age (yr) Age (yr) P =e -1.578-0.705Coast+0.307Age /(1+ e -1.578-0.705Coast+0.307Age ) where coast = 1 and coast= 0 Fishery Bulletin 98:612-624, Trans Am Fish Soc 141:1016-1025, MEPS 505:227-240
Landings and releases 800,000 Released alive 700,000 Landings Number of fish 600,000 500,000 400,000 300,000 200,000 On either coast, most of the snook are released. 100,000 0 1981 1983 1985 1987 1989 1991 1993 2,500,000 2,000,000 Released alive Landings Note: the vertical axes differ by coast. Number of fish 1,500,000 1,000,000 500,000 0 1981 1983 1985 1987 1989 1991 1993 Fig. 3.2.3
Total harvest Number of snook 160,000 Died subsequent to release 140,000 Landings 120,000 100,000 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 + 2.13% * Releases 0 1981 1983 1985 1987 1989 1991 1993 Number of snook 160,000 140,000 120,000 100,000 80,000 60,000 40,000 20,000 Died subsequent to release Landings 0 1981 1983 1985 1987 1989 1991 1993 North American Journal of Fisheries Management 21:70-75 Fig. 3.2.4
Fishing effort 3,000,000 2,500,000 2,000,000 Snook trips 1,500,000 1,000,000 500,000 0 1981 1983 1985 1987 1989 1991 1993 Source: National Marine Fisheries Service, Marine Recreational Information Program (MRFSS/MRIP) Fig. 3.3.1a
Sizes of retained fish Proportion 0.25 0.15 0.05 1986- - - 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 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, 26-34 in and -, 28-32 in on the coast and 28-33 in on the coast). 0.25 1986- - - Source: FWRI Snook program and MRFSS/MRIP Proportion 0.15 0.05 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 Total length (in) Fig. 3.4.1
Sizes of released fish Proportion 0.08 0.06 0.04 0.02 <= 12 n = 3565 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44+ 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 0.06 0.04 0.02 <= 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44+ Total length (in)
Ages of retained fish 0.40 0.35 - n=2,454 - n=2,550 Proportion 0.30 0.25 0.15 0.05 Ages of snook sampled in recent years under two slot limits (- 05, 26-34 in and -, 28-32 in. on the coast and 28-33 in on the coast). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Age (yr) 0.40 0.35 0.30 - n=4,870 - n= 786 Proportion 0.25 0.15 0.05 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Age (yr)
Ages of released fish Proportion 0.35 0.30 0.25 0.15 0.05 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 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. 0.35 0.30 0.25 Proportion 0.15 0.05 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Age (yr)
Abundance indices Number per seine haul 0.80 0.70 0.60 0.40 0.30 428 462 456 443 631 564 666 712 594 713 699 650 681 604 618 647 704 752 Number per seine haul 1.50 1.25 0.75 0.25 326 570 623 Fishery independent monitoring with a 183-m haul seine. 699 681 664 662 718 670 668 639 658 655 654 654 652 674 683 643 Fig. 4.1.1.1
Abundance indices Number caught per set or interview 3.50 3.00 2.50 2.00 1.50 FIM MRFSS/MRIP There is general agreement among the indices used for guiding the model. All of the indices showed a marked decrease in. 1986 1988 1990 1992 Number caught per set or interview 3.50 3.00 2.50 2.00 1.50 1981 FIM MRFSS/MRIP ENP 1983 1985 1987 1989 1991 1993 Fig.4.1.3
Assessment model Snook configuration of Age-Structured Assessment Program Version 3.0.17 (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
Benchmarks Transitional spawning potential ratio 0.80 0.70 0.60 0.40 0.30 2015 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 1986 1987 1988 1989 1990 1991 1992 1993 F SSB / R SSB / R F F 0 Transitional spawning potential ratio 0.80 0.70 0.60 0.40 0.30 2015 Assesssment Assessment Assessment Assessment 40% SPR 1986 1987 1988 1989 1990 1991 1992 1993 Fig. 4.2.2.4.8.1.2
Regional comparisons Number of snook per haul seine set 4.00 FIM 3.00 559 2.00 676 584 306 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 4.00 1459 MRFSS/MRIP Number per trip 3.00 2.00 6531 3003 1019 5344 Region Fig. 4.5.2
Regional comparisons Fishery independent haul seine catch rates by region Number of snook per haul seine 1 8.00 6.00 4.00 2.00 Tampa Bay 302 278 352 293 267 286 195 266 284 314 312 287 320 291 288 310 282 304 265 Number of snook per haul seine 1 8.00 6.00 4.00 2.00 Indian River 259 262 270 244 239 248 236 239 291 254 251 242 256 344 410 311 268 276 Number of snook per haul seine 1 8.00 6.00 4.00 2.00 208 230 135 210 224 Charlotte Harbor 208 216 216 214 208 210 205 207 204 212 206 206 206 206 1 8.00 6.00 4.00 2.00 137 200 192 192 189 192 196 241 254 200 222 176 141 146 160 144 144 148 Number of snook per haul seine Tequesta Fig. 4.5.3
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 (265-380 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 0.12 0.08 0.06 0.04 0.02 3.00 2.50 2.00 1.50 Temperature 1986 1987 1988 1989 1990 1991 1992 1993 Red tide Northeast Science 11:155-158 M.S. Thesis, University of Florida
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 350-910 mm TL and ages 2-14 years. Proportion 0.40 0.30 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 168 1045 mm TL and ages 1-10 years. We don t know how many snook die when these events occur. Proportion 0.60 0.40 0.30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Cold kill Age (yr) Cold kill 1 2 3 4 5 6 7 8 9 10 Age (yr)
Environmental effects Fishing mortality per year (age-7) Recruitment (number of age-1 fish, thousands) 2.50 2.00 1.50 3,000 2,500 2,000 1,500 1,000 500 0 1986 1987 1988 1989 1990 1991 1992 1993 1986 1988 Base w/environmental effects 1990 1992 w/environmental effects (half) Base Environment Mortality per year (age-7) Spawning biomass (mt) 2.50 Fishing mortality Natural mortality 2.00 1.50 1,600 1,400 1,200 1,000 800 600 400 200 0 1986 1988 1990 1992 Base w/environmental effects w/environmental effects (half) 1986 1988 1990 1992 After Fig. 4.2.2.4.8.2.3
Environmental effects Spawning biomass (mt) 700 600 500 400 300 200 100 0 1986 1987 1988 1989 1990 1991 1992 1993 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 1,000 800 600 400 200 0 1986 1987 1988 1989 1990 1991 1992 1993 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
Environmental effects 0.70 0.60 Unfished F40%SPR Fished spawning biomass per recruit (kg) 5.00 4.00 3.00 2.00 1986 1988 Base Enviromental effects 1990 1992 Kilograms per recruit 0.40 SSB/R F=0 0.30 SSB/R F 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Age (yr) tspr SSB/R F=0 F SSB / R SSB / R F F 0 5.00 The unfished SSB/R illustrates the impact of the environmental effects. Unfished spawning biomass per recruit (kg) 4.00 3.00 2.00 Base Enviromental effects 1986 1988 1990 1992 Fig. 4.2.2.4.8.2.4
Environmental effects benchmark Base Enviromental effects Transitional spawning potential ratio 0.80 0.60 0.40 40% SPR 1986 1987 1988 1989 1990 1991 1992 1993 Fig. 4.2.2.4.8.2.3
Benchmarks 1.50 1.50 1.25 1.25 F ratio (F gm /F 40%SPR ) 0.75 0.25 F ratio (F gm /F 40%SPR ) 0.75 0.25 0.25 0.75 1.25 1.50 1.75 2.00 SSB ratio (SSB /SSB 40%SPR ) 0.25 0.75 1.25 1.50 1.75 2.00 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 ) 1.50 1.25 0.75 0.25 0.25 0.75 1.25 1.50 1.75 2.00 SSB ratio (SSB / SSB 40%SPR )
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