Sharks in nearshore environments: models, importance, and consequences

Abstract

Resale or republication not permitted without written consent of the publisherPopulation models show that nearshore habitats are crucial for small coastal sharks such as juvenile lemon sharks Negaprion brevirostris. Photo: Alastair Harry -11, 2010 of high quantity and quality to both environment and economy, resulting in these areas being identified as significantly valuable ecosystems (Costanza et al. 1997). Close proximity to land allows easy accessibility to nearshore areas, resulting in these regions being susceptible to increased exploitation. Fishing is one of the major human impacts affecting nearshore waters and overfishing has resulted in the decline and/or collapse of some coastal ecosystems (Pauly et al. 1998, Jackson et al. 2001. Coastal development also has detrimental effects on nearshore areas through modification practices such as dredging, construction, and deforestation, which can cause large-scale habitat degradation or loss (Suchanek 1994, Vitousek et al. 1997. The estimated proportion of the world's total human population living within 100 km of the coast is 60% (Vitousek et al. 1997), with this value projected to be 75% within 60 km of the coast by the year 2020 (DeMaster et al. 2001). Due to increasing human population in coastal areas, it is likely that human pressure in these regions will continue and potentially increase. With increased pressure, it will be progressively more important to understand how species and communities use nearshore waters so that effective conservation and management can be implemented. In addition to anthropogenic influences, environmental impacts such as weather events result in erosion, scouring, habitat destruction, sediment movement, and increased turbidity in nearshore areas (Rodriguez et al. 1994, Masselink et al. 2008. Inter-annual climate anomalies (e.g. El Niño, La Niña, drought) can change the physical characteristics of nearshore environments making conditions less favourable for inhabitants (Mol et al. 2000, Abel et al. 2007). Since nearshore areas are highly dynamic and variable, as well as vulnerable to exploitation, species that inhabit these waters must either cope with the changes they face, adapt accordingly, or leave in order to survive. OPEN PEN ACCESS CCESSMar Ecol Prog Ser 402: 1Sharks are a key component of nearshore ecosystems, acting as top predators and utilising a high proportion of available energy (Cortés 1999). Since nearshore waters provide a wide variety of habitat characteristics, sharks can exploit regions with features that are optimal for survival. For example, young sharks may utilise shallow or low salinity environments to decrease predation risk (Simpfendorfer et al. 2005, Wetherbee et al. 2007 or to forage in areas where food resources are most abundant (Simpfendorfer & Milward 1993); adults may exploit habitats to target high quality prey items for diet and growth (Heithaus et al. 2002). Nearshore regions are also used in different ways by different shark species, and the characteristics and habitat type of a re...

Evaluating catch and mitigating risk in a multispecies, tropical, inshore shark fishery within the Great Barrier Reef World Heritage Area

“…Species of these families vary greatly both in their life histories and their utilisation of inshore habitats (Knip et al 2010). For example, many small to medium-sized carcharhinids (e.g.…”

Distributions of Sharks across a Continental Shelf in the Northern Gulf of Mexico

“…While many species appear to use coastal areas as outlined in Springer (1967), recent attention has focused on the importance of nearshore habitat throughout the ontogeny of smaller species of shark. A new theoretical population model suggests that species such as Atlantic sharpnose Rhizoprionodon terraenovae and blacknose Carcharhinus acronotus sharks inhabit nearshore areas throughout their lifespan, while not using these regions as discrete nursery areas (Knip et al 2010). Conversely, larger species such as blacktip shark Carcharhinus limbatus likely follow the original population model outlined by Springer (1967).…”

Fine-scale spatial and seasonal partitioning among large sharks and other elasmobranchs in south-eastern Queensland, Australia

“…The selection of habitat by sharks in coastal waters is believed to be influenced by environmental characteristics, resource abundance and presence or absence of other competing species (Knip et al 2010). Environmental characteristics that have been associated with the distribution of coastal elasmobranchs include tide, water temperature, salinity, dissolved oxygen, substratum type and depth (Speed et al 2010).…”

“…Studies that have examined spatial and temporal partitioning among elasmobranchs have typically focussed on juvenile sharks or smaller sharks in shallow-water habitats (Simpfendorfer and Milward 1993;Speed et al 2010). Elevated catches of juvenile sharks are often reported in subtropical waters during the summer, which is linked to the nursery role that inshore waters provide (Castro 1993;Knip et al 2010) and the role that water temperature appears to play in the onset and conclusion of shark pupping and nursery seasons (Pratt and Carrier 2001).…”