Fish and Fisheries in Estuaries. Группа авторов

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spawners that select spawning sites and features to assure retention or dispersal of eggs and larvae within the estuary and (ii) offshore spawners that spawn in areas favourable for dispersal and directional transport of early‐life stages towards estuarine nurseries. Descriptions of hydrodynamic processes and physical features supporting recruitment, including examples for estuarine fishes, are described in Section 3.3.1. Physical processes not only assure connectivity amongst habitats in the recruitment processes of estuarine‐dependent fishes (e.g. Pineda et al. 2007) but also support marine and estuarine productivity that are closely linked to trophodynamics in the early life of fishes (e.g. Cushing 1990).

       3.2.2.3 Foods of early‐life stages

      A review of young‐of‐the‐year fish diets for 47 estuarine species in the northeastern USA indicated seven categories of invertebrates were important prey (copepods, amphipods, mysids, decapod shrimp, polychaetes, crabs and insects/arachnids) (Able & Fahay 2010). Copepods were important prey for 33 species, amphipods for 27 species, mysids for 26 species, decapod shrimp for 21 species, polychaetes for 17 species, decapod crabs for 13 species and insects/arachnids for 11 species. Other prey categories frequently eaten were isopods, bivalves, gastropods, ostracods, invertebrate eggs, nematodes, cnidarians, algae and cladocerans. The occurrence of insects and arachnids in diets of juvenile estuarine fishes points to the potential importance of allochthonous foods for some species. The importance of microplankton and protists in larval fish diets, including estuarine fish larvae, has become clearer with the advent of improved diagnostic methods (e.g. Zingel et al. 2019).

      The importance of copepods in feeding by estuarine fish larvae is illustrated for the clupeid Clupea harengus in the Baltic Sea where the copepod Eurytemora affinis dominated the diet of larvae, with an annual occurrence of 58–92% (Arula et al. 2012a). The significance of copepods in the diet of larval C. harengus also is reported in other studies, although the copepod species eaten differed amongst regions. For example, E. affinis dominated in the Baltic Sea (Schnack 1974); Acartia spp. in the Blackwater Estuary, England (Fox et al. 1999); Pseudocalanus sp., Acartia sp., Temora sp., Oithona similis and Centropages sp. in the North Sea (Fossum & Johannessen 1979, Checkley 1982); and Calanus finmarchicus in the North Atlantic (Fiksen et al. 2002). In South African estuaries, larvae of the estuarine‐dependent clupeid Gilchristella aestuaria fed extensively on eggs of the dominant copepod P. hessi (Whitfield & Harrison 1996) and larvae of five species in families Clupeidae, Haemulidae, Monodactylidae, Mugilidae and Sparidae fed predominantly on copepods (Whitfield 1985). Rotifers can also be an important prey item for first‐feeding larvae of C. harengus in the Baltic Sea (Margonski et al. 2006). In the Baltic clupeid Sprattus sprattus, the copepod Acartia sp. is important in the larval diet (Voss et al. 2003, Dickmann et al. 2007) and seasonal comparison of prey fields suggested that cladocerans become increasingly important during the summer months.

       3.2.2.4 Predators

      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).

       3.2.2.5 Weather, climate and estuarine change

      Extreme weather events that already occur naturally and climate variability or change (Gillanders et al. 2022) that may exacerbate such weather events can act to elicit reproductive or recruitment responses either directly or indirectly (Vinagre et al. 2009, Feyrer et al. 2015, Houde 2016, Jeffries et al. 2016; Elliott et al. 2019). The events may cause temperature shifts, flooding, freezes and droughts and result in higher salinity in the estuary. Such events may produce episodic low dissolved oxygen, habitat destruction and poor water quality. Weather (event‐scale) as a factor may be more important in estuaries than in the ocean where effects of weather are diluted and buffered by the large surface area and volume. Event‐scale weather may be especially important with respect to wind‐induced advection and larval ingress into estuaries (Hare et al. 2005a, Schieler et al. 2014, Bruno & Acha 2015).

      Long‐term changes such as inter‐annual variability in ingress patterns of estuary‐associated fishes are

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