Occurrence and biological impacts of fishing gear and other marine debris in the Florida Keys

Abstract

Fishing constitutes one of the most significant threats to marine biodiversity and ecosystem function, documented by a growing body of information on the numerous impacts to populations, community structure, and habitats (Dayton et al., 1995; Roberts, 1995; Jennings and Polunin, 1996). Besides the more obvious effects on species population structure, fishing activities may also reduce the structural complexity of habitats or cause corresponding changes in ecological processes such as competition and predation (Russ, 1991; Jones and Syms, 1998; Auster and Langton, 1999). These patterns are most obvious in areas where explosives, poisons, or other destructive fishing methods are used (Hatcher et al., 1989). However, ecological effects can be expected in any area where traps, mobile fishing gear such as trawls, and, potentially, even large numbers of recreational fishers operate (Russ, 1991; Jennings and Lock, 1996). The Florida Keys (Monroe County, Florida) have a long history of commercial and recreational fisheries that target a great diversity of fish and invertebrate species using a multitude of gears (Tilmant, 1989; Bohnsack et al., 1994). In terms of volume of seafood landed, the Florida Keys is the most important area in the state in landings, dockside value, and numbers of commercial fishing vessels, especially for highly valued invertebrate fisheries (Adams, 1992). There are also significant, but largely undocumented effects of tens of thousands of recreational fishers (Davis, 1977), who target hundreds of species using mostly hook-and-line and spear guns (Bohnsack et al., 1994). Baseline data on fishing gear and other marine debris were collected as part of a larger assessment of benthic community structure in the Florida Keys National Marine Sanctuary, a large (9500 km) marine protected area bordering three national parks in southern Florida (Fig. 1). These data are particularly timely because this coastal ecosystem continues to experience a growing number of recreational fishers, and both commercial and recreational fishers exploit hundreds of invertebrates and fish species (Bohnsack et al., 1994; Ault et al., 1998). This study addressed several issues on marine debris occurrence in shallow-water coral reef and hard-bottom habitats. First, what is the spatial extent and frequency of remnant fishing gear at multiple spatial scales in the Florida Keys? Secondly, what factors, such as habitat type (depth) or management regime (closed or open to fishing) affect the spatial variability of marine debris occurrence? Thirdly, what are the biological impacts of marine debris, especially from remnant commercial and recreational fishing gear, on reef biota such as hard corals and sponges? Forty-five sites were surveyed southwest of Key West to Big Pine Shoal in the lower Keys region of the Sanctuary, spanning 60 km from southwest to northeast and 12 km from nearshore to offshore (Fig. 1). Sites were visited between July and August 2000 and were selected using a two-stage, stratified random sampling design (Cochran, 1977; Ault et al., 1999). Five of the 23 no-fishing zones (designated as sanctuary preservation areas (SPAs), research only areas (RO), and ecological reserves (ER)) in the Sanctuary were surveyed (indicated in Fig. 1). Based on the spatial distribution of coral reef habitat types (FDEP, 1998) and the depth limits of the zones, the following habitat strata were sampled: nearshore hard-bottom, mid-channel patch reef, offshore isolated patch reef, offshore aggregate patch reef, back reef and rubble/hard-bottom matrix, shallow fore reef (4–7 m depth), and deeper fore reef (8–12 m) (Table 1). Two random sites were sampled in each no-fishing zone, within a particular habitat stratum that consisted of predesignated 200 200 m areas randomly selected from a grid constructed using a geographic information system. Corresponding author.