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Flathead grey mullet - West coast of USA Florida
Fact Sheet Title  Fact Sheet
Status of stocks and resources 2019
Flathead grey mullet - West coast of USA Florida
Fact Sheet Citation  
Owned byFood and Agriculture Organization (FAO) – ownership
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Species List:
Species Ref: en - Flathead grey mullet, fr - Mulet à grosse tête, es - Pardete, zh - 鲻
ident Block Flathead grey mullet - West coast of USA Florida
Aq Res
Biological Stock: Yes         Value: National
Management unit: Yes        Reference year: 2013
 
 
Aq Res State Trend
Aq Res State Trend
Aq Res State Trend
Aq Res State TrendNot applicable
Aq Res State TrendNot applicable
Aq Res State Trend
Aq Res State TrendMaximally sustainably fished

In Florida the assessment indicated that stocks (west and east coasts) were not overfished and that overfishing was not occurring. 
Habitat Bio
Climatic Zone: Tropical; Temperate.   Vertical Dist: Demersal.  

Water Area Overview
Spatial Scale: National

Water Area Overview
Aq Res Struct
Biological Stock: Yes
Bio Assess
Uncertainty: Intermediate


A suite of analytical models of various forms were used to assess the status of striped mullet in Florida. The assessment models varied from data poor methods (depletion-based stock reduction analysis) to more complex models such as a nonequilibrium surplus production model (ASPIC), delay difference, stochastic stock reduction analysis, and stock synthesis. The depletion-based stock reduction analysis (DBSRA) method relies solely on removals data. The stochastic stock reduction (SSRA) and surplus production (ASPIC) models both include landings as well as indices of abundance and catch rate data. The delay-difference model (DD) is a simple age structured model that includes two ages, recruits and adults. This move towards non-age structured models is because the fishery-independent monitoring (FIM) trammel-net survey, which provided the age samples, was terminated and the spatial and temporal coverage from fishery-dependent sampling was inadequate. Lastly, we constructed a stock synthesis model that includes historical removals, indices of abundance, length composition, and age composition. data when available.
Data

Data up to 2013. Landings from the west coast of the state of Florida represent approximately 25% of total landings from FAO Area 31. NMFS landings in 2014 similar to 2013 with Significant drop (~50%) in 2015 and 2016. Analyses of fishery-dependent data were based on commercial landings reports (1978-1984) from the NMFS general canvass database, commercial landings and trip information (1985-2013) from the FWC-FWRI’s Marine Fisheries Information System (Trip ticket) database, biostatistical information (e.g., lengths) from the Trip Information Program (TIP, 1991-2013) database, and recreational landings estimates and length information from the NMFS-MRFSS (1981-2003) and NMFS-MRIP (2004-2013) databases. Additionally, commercial landings (1870-1977) reports were compiled from various sources including the U.S. Commissioner of Fisheries and Florida State Board of Conservation. 
Assess Models
Type:  Age-structured
Depletion-Based Stock Reduction Analysis

The DBSRA is a catch-based model developed by Dick and MacCall (2011). The DBSRA is primarily used in “data poor” stock assessments. The input data are limited to time series of harvest, estimates of age at maturity, an initial value of unfished biomass (K), and prior distributions of four leading parameters: natural mortality rate (M), the ratio of FMSY to M (FMSY/M), the relative biomass at maximum latent productivity (Bmnpl = BMSY/K), and assumed current depletion level (Bcurrent/K). For this assessment, the DBSRA model was based on the total harvest (commercial and recreational) of striped mullet during 1956-2013 in the east coast and during 1930-2013 in the west coast (Table 1).
Stochastic Stock Reduction Analysis

The SSRA is essentially an exploratory tool used to derive likely estimates of important management parameters, e.g. FMSY and MSY, given the observed persistence of the exploited population through time. The estimated trends in exploitable biomass are contrasted with the available overall fishery catch rates to help estimate the likely management parameters. In this approach, an age structured population model with Beverton-Holt stock-recruitment function is simulated forward in time from the beginning of the catch time series, removing annual harvest, adding recruitment and subtracting mortality, so as to produce a cumulative prediction of current stock size (Walters et al. 2006). We used an ADMB version of SSRA developed at FWRI (Cooper, personal communication) largely based on computer codes developed by Walters et al. (2006) and Martell et al. (2008).
Assess Models
Type:  Biomass-aggregated
Non-Equilibrium Surplus Production (ASPIC)

Surplus production models are used to describe the dynamics of a fished stock in terms of biomass by simply using the previous year’s biomass, growth in biomass in that year, and catch. Input data for each run included total landings (commercial and recreational,1985-2013), standardized commercial CPUE for the pre (1985-1994) and post (1995-2013) net ban periods, and initial starting values for B 1/ K, K, q, and MSY. The ASPIC model measures the uncertainty associated with the F/FMSY and B/BMSY estimates using a bootstrapping routine.
Assess Models
Type:  Others
Delay-Difference

The DD is an intermediate (partially age-structured) modeling approach developed initially by Deriso (1980) and further modified (generalized) by Schnute (1985). It allows age-structured population dynamics to be simplified to a single equation involving total biomass and numbers. The DD requires information on body growth, recruitment, and survival. The main advantage of the delay difference equations over full age-structured accounting is that they can be solved very quickly for very large numbers of populations, e.g. in spatial grid models, without loss of age-structure effects on average size of fish harvested and on fecundity. The continuous version of delay-difference model was also applied under the assumptions that reproduction, recruitment, growth, and mortality rates are all varying continuously over time.
Assess Models
Type:  Size-structured
Stock Synthesis

Stock synthesis, SS, is a forward projecting age and size structured assessment model that can be fit to various fishery and survey data (Methot 2000). Growth parameters are specified explicitly, selectivity patterns can be a function of size and/or age, and weight-at-age is determined from size-selectivity and size-at-age probability. The population model controls the rate at which new individuals recruit to the population, the mortality rates (fishing and natural), the growth rates, and reproduction. Stock synthesis then fits the model to observed catch-at-age and –length data from the surveys and fleets as well as indices of abundance from fishery independent or dependent sources. It accounts for the influence of sample size and factors such as aging error on relationship between samples and actual observations.
Results

Conclusions, Stock Status - All five modeling approaches used in this assessment show that fishing mortality rates declined sharply after the 1995 net-ban and have remained at low levels in recent years in both coasts of Florida. This is consistent with significant drops in landings and fishing effort since the 1995 net-ban. Commercial landings have declined from an annual average of 28 million pounds during 1930-1994 to an annual average of 8.8 million pounds during 1995-2013, a 70% reduction in landings after the net-ban. The fishing effort (number of one-day trips) declined from an annual average of 59,399 trips during 1985-1994 to an annual average of 25,288 trips during 1995-2014, a 57% reduction in fishing effort after the net-ban. Presently, the Florida Fish and Wildlife Conservation Commission, has adopted a target spawning potential ratio (SPR) of 35% (FSPR35%) for striped mullet in Florida. The estimates of current fishing mortality rates relative to FSPR35% (F/FSPR35%) or relative to FMSY (F/FMSY) were below 1 from all five models, suggesting that overfishing is not occurring in either coast of Florida (Table 8). Estimates of current biomass relative to the biomass level at FSPR35% or relative to BMSY (B/BMSY) were above 1 from all five models, suggesting that mullet stocks are not considered to be overfished in Florida (Table 8). Estimates of the SPR from the SS3 model showed that SPR varied between 15% and 25% prior to the 1995 net-ban and then increased sharply to above the 35% target level after 1995, varying around 0.45 on the east coast and around 0.5 on the west coast (Figure 44A and Figure 52A). Phase plots from the delay difference and SS3 models (Figure 31, Figure 34, Figure 44B, and Figure 52B) indicated that mullet stocks are considered healthy in both coasts of Florida given recent fishing mortality rates and biomass levels. The SSRA, ASPIC, delay difference, and SS3 models assumed that the standardized CPUE were a reliable index of adult population abundance, although greater weighting was allowed for the catch. Results from these models were heavily dependent on the trends observed in the catch and CPUE indices given lack of strong signals in the length and age composition data. Because of limited direct aging data from the fishery, the catch-at-age matrices were constructed primarily based on age length keys (ALK) derived from biological studies and fishery-independent samplings. Consequently, the age structures to which the models were fit for this assessment may not be representative of a particular year because the pooled ALK would tend to minimize apparent differences among years. In addition, the pooled ALK would underestimate apparent decline in older age over time and or the influence of weak or strong year classes. 
Sci Advice

Research Recommendations - • It is critical that future sampling and data collection for striped mullet assessment include direct age sampling of the commercial and recreational catches with sufficient spatial and temporal resolutions. Since the net ban, commercial gill nets of various mesh sizes have been replaced by cast nets and small seines. The age data from various sectors of the fishery should be incorporated into assessment for accurate measurements of the gear selectivity patterns. Future data collection should also include comprehensive on-board observations for characterizing the spatial and temporal patterns in fishing activities and effort in the mullet fishery. Finally, fishery independent samplings should be conducted to update estimates of biological and population parameters needed for calibrating the stock assessment models. • Because mullet are important in the flow of energy through estuarine and coastal communities and are exposed to high level of predation, future modeling approaches should include predation-prey interactions and the influence of the bottom-up processes. An ecosystem-based or multispecies approach will provide quantitative estimates of predation and natural mortality rates, important parameters estimates for a forage species such as mullet. • Findings from all five modeling approaches support the general conclusion that while there is uncertainty about model outputs, the SPR estimates have been above the 35% SPR target in recent years in Florida. The future condition of mullet stocks depends on market demand, landings levels and fishing effort, and environmental condition affecting the stock and recruitment fluctuations. Commercial landings levels in the past ten years seem to indicate that landings have stabilized between 1-1.5 million pounds annually on the east coast and between 8-9 million pounds annually on the west coast. Given recent landings and fishing effort levels, fishing mortality rates should stabilize or decline further if recoveries of mullet stocks continue at the present rate.
Management
Management unit: Yes
Sources
 
FAO. Western Central Atlantic Fishery Commission. 2019. Review of the state of fisheries and fisheries resources in the WECAFC region. Meeting document WECAFC/SAG/IX/2018/3 of the ninth session of the Scientific Advisory Group, Christ Church, Barbados, 19-20 November 2018.  Click to openhttp://www.fao.org/fi/static-media/MeetingDocuments/WECAFC/SAG2018/3e.pdf
Chagaris, D., Addis, D. & Mahmoudi, B. 2014. The 2014 stock assessment update for striped mullet, Mugil cephalus, in Florida. Florida Fish and Wildlife Conservation Commission, 76 pp.  Click to openhttps://myfwc.com/media/13333/stripedmullet-assessment-2014-final.pdf
Bibliography
 
FAO. Western Central Atlantic Fishery Commission/FAO Commission des pêches pour l’Atlantique Centre-Ouest/FAO Comisión Central de Pesca para el Atlántico CentroOccidental. 2019. Report of the ninth session of the Scientific Advisory Group, Christ Church, Barbados, 19-20 November 2018. Rapport de la neuvième session du Groupe scientifique consultatif, Christ Church, Barbade, 19-20 Novembre 2018. Informe de la octava sesión del Grupo Asesor Científico, Christ Church, Barbados, 19-20 de Noviembre de 2018. FAO Fisheries and Aquaculture Report/Rapport sur les pêches et l’aquaculture/Informe de Pesca y Acuicultura. No. 1266. Bridgetown, 156 pp.  Click to openhttp://www.fao.org/3/ca4776t/ca4776t.pdf
All references to figures, tables and bibliography in the text are found within the source of information.
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