Florida Releases Updated Snook Stock Assessment
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The 2013 Stock Assessment Update of Common Snook,
Centropomus undecimalis
Robert G. Muller and Ronald G. Taylor
Florida Fish and Wildlife Conservation Commission
Fish and Wildlife Research Institute
100 Eighth Avenue Southease
St. Petersburg, Florida 33701-5020
June 5, 2013
EXECUTIVE SUMMARY
- This assessment update includes data through 2012, albeit the 2012 data are preliminary.
- Because of a severe cold spell in January 2010, the snook
fishery remained closed by executive order until 31 August 2010. The
fishery briefly opened on 1 September 2010 but was closed again by
executive order on 17 September 2010 until 31 August 2011. The fishery
on the Atlantic coast opened 1 September 2011 but the fishery on gulf
coast has remained closed to harvest; however, the executive order
keeping the fishery closed expires 31 August 2013.
- In 2012, based on recreational interviews with anglers who
indicated the type of fish that they were targeting, snook dropped to
the tenth most targeted species on both coasts (down from fifth place in
2009 on the Atlantic coast and from third place in 2009 on the gulf
coast).
- As in previous assessments, total catch rates for MRFSS-MRIP
and Everglades National Park creel data were calculated with generalized
linear models. The variables that significantly reduced the deviance in
the estimated catch rates included: for MRFSS-MRIP,-year, two-month
wave, time fished, fishing mode, and fisher avidity and for the
Everglades National Park creel survey, catch rates the variables were
year, month, time fished, and area fished.
- On the Atlantic coast, recreational total-catch rates were
flat from 1996 through 2009 then dropped in 2010 and 2011 and a slight
increase in 2012 while the catch rates on the gulf coast were generally
increasing until the drop after the 2005 red tide event then again the
rates were increasing until a severe drop in 2010 and modest increases
after.
- Total catch rates from the Everglades National Park creel
survey, which were applied to the gulf coast analyses, showed similar
increases in recent years as did the recreational index for the gulf
coast and catch rates in the park also experienced the sharp drop in
2010 followed by increases afterwards.
- The fishery-independent haul seine catch rates in numbers of
snook per set provided by the FWC's Fishery Independent Monitoring
program on the Atlantic coast decreased from 1997 to 2001 and then were
stable until the drop in-2010, afterwards the catch rates increased
slightly while catch rates on the gulf coast from 1996 to 2008 were
mostly stable and then dropped in 2009 and 2010 to the lowest catch rate
in the series. The gulf catch rates on the gulf increased after 2010.
We used length data by coast for age-2 fish from the fishery independent
samples to identify age-2 fish in the seine hauls and then repeated the
standardization process to generate indices just for age-2 fish by
coast. The patterns in age-2 fish resembled the adult catch rates.
- The sizes of fish that anglers released were estimated from
angler interviews, logbooks, the Snook and Gamefish Foundation's Angler
Action Program, and a fishery independent catch-and-release fishing
program. Data from the first three programs were available beginning in
2002 and the Angler Action Program beginning in 2010. The fishery
independent catch and release fishing program operated from 2002 through
2005. We used the average lengths from 2002-2005 by coast to assign
lengths to the released fish in the years 1999 to 2002 and fish less
than 24 in TL for the earlier years.
- As with the 2012 assessment, we used the National Marine
Fisheries Service's Age-Structured Assessment Program (ASAP) because
ASAP is more flexible than the previously used Integrated Catch-at-Age
model especially in terms of numbers of indices, years with age data for
estimating selectivity, linking discards to their fisheries,
differential weighting of population parameters, and other technical
details.
- Fishing mortality rates on the Atlantic coast tracked those
estimated in earlier assessments until 1998 and then the rates were
higher for 1999-2003 and then similar from 2004 and later. After the
extended season closure, from January 2010 until September 2011 on the
Atlantic coast, the estimate of average fishing mortality for reference
age (age-
was 0.49 per year in 2011 and 0.15 per year in 2012. On the
gulf coast, the fishing mortality rates declined after the slot limit
was implemented in 1999 and the fishing mortality for the reference age
(age-7) was 0.04 per year in 2010 which was down from the 1997 high
value of 0.76 per year. The fishing mortality rate during the closure
was 0.075 in 2011 and 0.066 per year in 2012. Most of the mortality on
the gulf coast came from release mortality. - The estimated recruitment on the Atlantic coast in 2007
through 2011 was the lowest over the 27 year time period and recruitment
on the gulf coast from 2005 through 2009 was the lowest since 1992. The
low numbers of recruits on the gulf coast occurred at the highest
spawning biomass values. Low recruitment stemming from high spawning
biomass indicates that environmental effects are important determinants
of year class strength.
- The spawning biomass of snook decreased on the Atlantic coast
until 2001 and then has slowly increased until 2010 and then decreased
again. The spawning biomass on the gulf coast increased over the time
series until 2010 then dropped and was a little lower in 2012 followed
by an increase in 2012.
- In July 2007, the Commission implemented the Snook Work
Group's recommendations to adopt a one-fish bag limit statewide and to
narrow the slot limits to 28-32 inches total length (TL) on the Atlantic
coast and 28-33 inches TL on the gulf coast. Bag limit adherence was
higher on both coasts. During 2008-2012, only three out of 1,874 anglers
intercepted on the Atlantic coast (two out of 1,169 trips) kept more
than one fish per angler while during the period 2002-2012 on the gulf
coast, thirteen out of 8,125 anglers intercepted on the gulf coast
(seven out of 6,491 trips) kept more than one fish per angler. Based
upon the average lengths of kept fish recorded recreational samplers for
the 2008-2012 time period, anglers on the Atlantic coast had reasonable
compliance with 82% of the kept fish being within the 28-32 in slot
limit and anglers on the gulf coast had less compliance with only 59% of
the kept fish being within the 28-33 in slot limit. On the Atlantic
coast 5% of the fish were undersized (less than 28 in) and 13% were
oversized (greater than 32 in) while on the gulf coast 39% of the fish
caught were undersized and only 2% were oversized (greater than 33
inches).
- The Commission's management objective for snook is to maintain the spawning potential ratio (SPR) at or above 40%. The transitional SPR (tSPR) values in 2012 approached the Commission's objective on the Atlantic coast (34%) and exceeded their objective on the gulf coast (5












