Читать книгу Fish and Fisheries in Estuaries - Группа авторов - Страница 82

Human‐caused catastrophes, although relatively uncommon, may reduce reproductive success of estuarine fish populations. The increasingly heavy use of coastlines and estuaries by humans has elevated the risk from hazards, both man‐made and natural (Elliott et al. 2014). Hazards that lead to catastrophes often are acute events, e.g. toxic spills that could kill early‐life stages of fishes or, alternatively, catastrophes may evolve from chronic stressors that have long‐term impacts on habitat and severely reduce reproductive capacity. Amongst the best documented events are those caused by spills of oil in the coastal ocean and estuaries. One of the largest known catastrophes of human origin, the Deepwater Horizon oil spill in the Gulf of Mexico, did not result in any clear effects of the oil on marsh fish population abundance (Able et al. 2015). Nor was it possible to confidently understand negative effects on individuals versus populations, indicating critical knowledge gaps (Fodrie et al. 2014). However, there were clear changes in gene expression and associated gill immunochemistry (Whitehead et al. 2012) that could be indicative of stress on future reproduction. A similar difficulty in interpreting catastrophic effects occurred when trying to evaluate the response of estuarine fishes to Hurricane Sandy in Barnegat Bay (USA) in the Mid‐Atlantic (Valenti et al. 2020).

In southern Africa, the loss of Lake St Lucia as a fish nursery area, particularly for estuary‐associated marine fish species, primarily due to freshwater deprivation and the subsequent evaporation of more than 90% of the surface area of this 35 000 ha estuarine lake ranks as a major catastrophe for coastal fishes (Cyrus et al. 2010). The prolonged closure of the St Lucia Estuary mouth due to human‐induced, inadequate river inflow to the lake has deprived the system of larval and juvenile marine and catadromous fish ingress (Cyrus & Vivier 2006). This loss has impacted the abundance of coastal marine fish species that normally use the St Lucia system as a nursery area (Mann & Pradervand 2007).