EvalUatiNG MaNaGEMENt aCtioNS for SPottEd SEatroUt, cYNoScioN NEBULoSUS, iN MiSSiSSiPPi witH aN aGE-StrUCtUrEd ProjECtioN ModEl

Spotted seatrout, Cynoscion nebulosus, is an important recreational fishery in the coastal waters of the Gulf of Mexico and is the most sought after gamefish in coastal Mississippi. The management of C. nebulosus is state-specific, and unlike other similarly managed species, data on both population structure and movement support the existence of local sub-stocks. It is important for each state to clearly examine its own sub-stock in the context of its own state fishery in order to properly manage for local sustainability. We used an age-structured assessment model to examine the status (1993–2005) of the Mississippi C. nebulosus population and to project forward several probable management actions (i.e., length limits) while also accounting for uncertainty in both fishing mortality and annual recruitment. Model results suggest annual fishing mortality for Mississippi C. nebulosus is close to Fmsy, but that spawning stock biomass (SSB) is not below SSBmsy. This suggests the sub-stock is currently stable, but with high fishing pressure and a high dependence on annual recruitment to the fishery. Projections suggest that when uncertainty in angler effort and annual recruitment are included in the analysis, more conservative management actions are warranted in order to achieve both higher fishery yield and stable SSB. IntroductIon Spotted seatrout, Cynoscion nebulosus, is an important recreationally and commercially harvested species in all states bordering the northern Gulf of Mexico (GOM, GSMFC 2001). In particular, the landings of C. nebulosus have been increasing in coastal Mississippi state waters since 1995 as spotted seatrout are the dominant target of recreational anglers within the state. While historically the commercial harvest of C. nebulosus has been high, recreational landings have represented over 90% of total landings since 1981 (NMFS Fisheries Statistics Section unpublished data). As a result, the recreational management of C. nebulosus in Mississippi is a significant issue that receives a lot of public attention. Although C. nebulosus is harvested across the northern GOM coast, there is evidence that there is not a single GOM stock but multiple sub–stocks. Cynoscion nebulosus is a non–migratory estuarine–dependent species (Gold and Richardson 1998) that can be found in a variety of coastal habitats, but is generally found in shallow water (< 1 m) associated with rooted vegetation (GSMFC 2001). Data from tagging studies in Mississippi and elsewhere indicate that individual adult fish are highly unlikely to travel more than 15 km both within and between years (Moffett 1961, Baker and Matlock 1993, Hendon et al. 2002). These data support the idea that there are sub–stocks of C. nebulosus differentiable at a scale consistent with each GOM state, and it is reasonable to generate both independent stock assessments and management regulations for each GOM state. This is consistent with existing management in that C. nebulosus are managed independently within each state as a part of a cooperative agreement between states (GSMFC 2001). Regulations for the recreational harvest of C. nebulosus vary greatly by GOM state (Table 1). Yet, all five states have adopted a proxy for maximum sustainable yield (MSY) based on the spawning potential ratio (SPR). The SPR measures the reproductive potential of the fished stock in comparison to the reproductive potential of the virgin (i.e., unfished) stock. The SPR proxy can be estimated from agestructured landings data and provides an easily interpretable benchmark against which to determine stock status. Not all states have a target SPR value but all 5 states report the SPR for their state as part of their respective stock assessment. The recreational fishery for C. nebulosus in Mississippi is particularly important in comparison to other state–managed fisheries. An analysis of angler interview data for Mississippi indicates that C. nebulosus is the dominant target species among anglers in Mississippi (National Marine Fisheries TABLE 1. Current fishery regulations for Cynoscion nebulosus by Gulf of Mexico (GOM) state. SPR—spawning potential ratio. State Minimum size Daily Bag Target SPR limit (in) limit Florida 15-20* 5 35%