Читать книгу Fish and Fisheries in Estuaries - Группа авторов - Страница 45

The role of predation in estuarine food webs has been frequently researched (Crowder et al. 1997, Juanes et al. 2002, Krause et al. 2002, Craig et al. 2007), but we still lack a unifying understanding of major predators and their roles in controlling or regulating fish recruitment. The frequency of predation on larval and juvenile stages of fishes is evident from a summary of adult and juvenile fish stomach contents in temperate estuaries of the US east coast. In this summary, larval and juvenile fishes were important prey in 34% of the species analysed, and they occurred in the diet of 72% of the analysed species (Able & Fahay 2010). There are limits to evaluating predation from a visual approach in gut analysis on predators, especially for small, easily digested fish eggs, larvae and small juveniles. For example, the evidence of piscivory by Fundulus heteroclitus was limited by fast digestion times of small conspecifics, with this prey unidentifiable in 1 hour and completely evacuated in 6–7 hours (Able et al. 2007). Furthermore, significant spatial variation in diets, as along estuarine salinity gradients (Able et al. 2017), occurs for some large predators and can confound understanding of this source of mortality.

Small fishes and jellyfish taxa are amongst the most important predators on early‐life stages of fishes (Purcell & Arai 2001). In Chesapeake Bay, the ctenophore Mnemiopsis leidyi, the cnidarian Chrysaora chesapeakei (previously C. quinquecirrha) and planktivorous fishes were demonstrated to be important predators on larvae of Anchoa mitchilli and Gobiosoma bosc (Cowan & Houde 1992, 1993, Breitburg et al. 1994, Purcell et al. 1994). In the Baltic Sea, demersal eggs of Clupea harengus are vulnerable to resident fish predators, e.g. Gasterosteus aculeatus and Neogobius melanostomus (Kotterba et al. 2017b).

Environmental factors may modify ability of predators to consume fish eggs and larvae. For example, under low dissolved oxygen conditions, jellyfishes increased their predation capability on estuarine fish larvae, while pelagic fishes had reduced capability (Breitburg et al. 1994, Shoji et al. 2005a). Piscivores, mostly fishes but also birds and mammals, are an important source of mortality to juveniles of estuarine forage fishes (Baker & Sheaves 2009b, Able & Fahay 2010). In another example of predation on juveniles of estuarine fishes, predation by large Morone saxatilis occurs on smolts of Salmo salar in Canadian systems (Daniels et al. 2018). Moreover, large piscivores can consume substantial quantities of young‐of‐the‐year individuals that are pre‐recruits of species exploited in managed estuarine fisheries, as reported for Chesapeake Bay (Ihde et al. 2015).