This is Part two of my series on Adaptive Management in Recreational Fisheries. This installation will introduce a candidate model species, Spotted Seatrout (Cynoscion nebulosus), for marine stock enhancement. Learn about the Science Consortium for Ocean Replenishment (SCORE) here. Part one touched on the global importance of fish, and the growing demand for developing a comprehensive approach to fisheries management. If you have not read Part one and would like to, you can find a link to it here.
Why Spotted Seatrout (Specs)?
The Spotted Seatrout is the most popular recreational species in the Gulf of Mexico (GoM), and represented 45% of the fish caught recreationally in 2011 (Fulford and Hendon 2010, NMFS 2011). Its euryhaline nature (having a high tolerance for changes in salinity) allows it to have a wide distribution largely affiliated with the coastal habitats throughout the entire GoM. The Spotted Seatrout’s affinity for estuarine and near shore environments make it easily accessible, and its aggressive temperament, tendency to fight, and high quality flesh make it highly prized by anglers.
Although Spotted Seatrout stocks are currently considered stable, high annual harvest rates of Spotted Seatrout evoke concerns about population dynamics. Since the initiation of recreational saltwater fishing license in July 1993, total license sales have increased approximately 13%. Fishing mortality is now considered to be approaching that of maximum sustainable yield (Fulford and Hendon 2010), yet recreational fishing efforts have increased an average of 7% annually since 1993 (Fulford and Hendon 2010).
The Spotted Seatrout is most commonly associated with shallow, brackish water bays and estuaries that contain extensive submerged vegetation and adjacent deep water refuges from extreme summer and winter temperatures (Zieman 1982). Although seagrasses such as Halodule spp. and Thalassia spp. appear to be critical habitat for the early developmental stages of Spotted Seatrout, tidal creeks, bayous, marshes, and other areas that may be lacking extensive seagrass beds can also provide adequate habitat for juveniles (McMichael and Peters 1989, Killam et al. 1992). Perhaps a larger driving factor in the distribution of the species than association with a particular habitat type is the mere presence of a structural component, which varies throughout the Gulf of Mexico’s coastal environments.
The Spotted Seatrout has been characterized as an opportunistic carnivore that feeds primarily on small crustaceans during larval and juvenile life stages and fish and shrimp during adult life stages (Pearson 1929, Gunter 1945, Perret et al. 1980). Primary components of the Spotted Seatrout diet vary based on fish size, habitat type, and season; however, food availability may be the most influential factor mediating food selection (Gunter 1945, Tabb 1961, Tabb 1966, Rogillio 1975, Perret et al. 1980, McMichael and Peters 1989).
Tagging studies have shown that the Spotted Seatrout is non-migratory and estuary-specific, with limited movement between estuaries. Tagging data also have shown that Spotted Seatrout is recaptured primarily in the same area as tagged and released. In one study, movement was generally less than 32 km (Warren et al. 1998). Movement patterns are most likely strongly associated with food availability and prey movements (Guest and Gunter 1958, Rogillio 1982). Fall movement of Spotted Seatrout paralleled the movement patterns of Gulf Menhaden into up-river locations (Deegan and Thompson 1985). Seasonality also influences spawning movements out of bays and bayous to deeper coastal waters in spring, although regional spatial variations do exist (Deegan and Thompson 1985).
Spotted Seatrout spawning is controlled by temperature, salinity, and photoperiod (Lorio and Perret 1980); however, spawning occurs over a wide range of salinities from 10-40 mg/L (Brown-Peterson 2003). For reference, full strength seawater is 35 mg/L. Although grass beds are believed to be important, there is no true consensus on essential habitat for Spotted Seatrout spawning (Brown-Peterson et al. 1988). Brown-Peterson (2003) noted that the Spotted Seatrout is a multiple spawner with two spawning peaks, May and August, during which they can spawn 8-11 times (Saucier and Baltz 1993).
Spotted Seatrout eggs vary in size, ranging from 0.7-0.98 mm in diameter (Miles 1951), and can be found over a wide range of salinities in marine or estuarine environments (Kucera et al. 2002). In aquacultural settings, larvae hatch about 18 hours after egg 6 fertilization (Fable et al. 1978). First feeding in an aquaculture setting starts after absorption of the yolk-sac, usually 72-80 hours post-hatch (Arnold et al. 1976). In the wild, larvae ranging from 2-6 mm are pelagic, similar to eggs, and found throughout bays (Powell et al. 1989). Older larvae, ranging from 6-18 mm, settle to the bottom and are closely associated with structural habitats in estuarine environments (Brown 1981, Rooker et al. 1998). McMichael and Peters (1989) found that larvae settle to the bottom from plankton at about 7 mm (17 days old). Copepod nauplii are the predominant food source for Spotted Seatrout larvae <15 mm (McMichael and Peters 1989). Larger larvae selected prey items such as adult copepods, amphipods, and mysid shrimp (McMichael and Peters 1989). A dietary shift away from copepods and amphipods toward larger prey items such as fish and shrimp occurs at about 60 mm (Mason and Zengel 1996). Lorio and Perret (1980) noted that adult Spotted Seatrout >350 mm preferentially seek out fish.
Although Spotted Seatrout make for a great model species for testing the efficacy of marine stock enhancement, many issues and set-backs have befallen stock enhancement research. One of the main issues encountered has been lack of recapture data once the hatchery-reared Spotted Seatrout have been released into the wild. Part three will discuss the issues in more detail.
Learn about the Science Consortium for Ocean Replenishment (SCORE) here
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