Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science

The fishery for spiny lobster Panulirus argus in the Florida Keys National Marine Sanctuary is well chronicled, but little information is available on the prevalence of lost or abandoned lobster traps. In 2007, towed-diver surveys were used to identify and count pieces of trap debris and any other marine debris encountered. Trap debris density (debris incidences/ha) in historic trap-use zones and in representative benthic habitats was estimated. Trap debris was not proportionally distributed with fishing effort. Coral habitats had the greatest density of trap debris despite trap fishers’ reported avoidance of coral reefs while fishing. The accumulation of trap debris on coral emphasizes the role of wind in redistributing traps and trap debris in the sanctuary. We estimated that 85,548± 23,387 (mean±SD) ghost traps and 1,056,127± 124,919 nonfishing traps or remnants of traps were present in the study area. Given the large numbers of traps in the fishery and the lack of effective measures for managing and controlling the loss of gear, the generation of trap debris will likely continue in proportion to the number of traps deployed in the fishery. Focused removal of submerged trap debris from especially vulnerable habitats such as reefs and hardbottom, where trap debris density is high, would mitigate key habitat issues but would not address ghost fishing or the cost of lost gear. According to the United Nations Environment Programme, as much as 70% of the global input of marine debris sinks to the seafloor in both shallow coastal areas and much deeper parts of the ocean (UNEP 2011). Many factors influence localized accumulation of debris, including size of debris items (e.g., length of a piece rope), bottom topography (e.g., ledges, crevices), oceanographic processes (e.g., tides, circulation Subject editor: Anne Hollowed, Alaska Fisheries Science Center, Seattle *Corresponding author: tom.matthews@myfwc.com Received November 27, 2012; accepted September 29, 2013 patterns), meteorological events (e.g., hurricanes), distribution of fishing effort, and level of boating activity (June 1990; Galgani et al. 1995, 1996; Hess et al. 1999; Moore and Allen 2000; Acha et al. 2003; Boland and Donohue 2003; Katsanevakis and Katsarou 2004; Chiappone et al. 2005; Uhrin et al. 2005; Bauer et al. 2008; NOAA 2009). In a review of the literature on benthic marine debris, more than 60% of the 20 D ow nl oa de d by [ C cf hr B ea uf or t L ab ] at 1 1: 09 0 2 Ju ne 2 01 4 LOBSTER TRAP DEBRIS IN FLORIDA KEYS 21 studies cited marine activities (e.g., shipping, fishing) were the primary source of benthic debris worldwide (Spengler and Costa 2008). Although the contribution of abandoned, lost, or otherwise discarded fishing gear to marine debris has long been recognized worldwide, quantitative data on this debris are sparse for many regions (Macfadyen et al. 2009). In 2007, 25,370 pleasure boats and 2,653 commercial vessels were registered in the Florida Keys (FLHMSV 2007), providing ample possibilities for intentional or unintentional littering and loss of gear and equipment, debris likely to settle on the seafloor. A large majority of registered commercial vessels target the spiny lobster Panulirus argus fishery (Milon et al. 1998; U.S. Office of the Federal Register 2011). Over the past 10 fishing seasons (2003–2012), the number of traps permitted annually in this fishery averaged 493,000. Lobster fishers reported that they lose 10–28% of their actively fished traps in nonhurricane years (Matthews and Uhrin 2009). The law requires that all lobster traps have an attached surface buoy; buoy lines are a navigational challenge in this region of high boat traffic and are often severed by boat propellers. The resulting absence of surface demarcation leads to impaired trap relocation and gear loss. Other causes of loss are vandalism, theft, entanglement of gear on the bottom, inability to relocate traps, and gear degradation. Although Florida lobster fishers are required by law to retrieve their traps before the close of the season, some abandonment of traps occurs. Strong winter storms, tropical storms, and hurricanes greatly exacerbate gear loss. Respondents of a mail survey reported a lobster trap loss of approximately 60% during the 2005–2006 fishing season when three hurricanes (Katrina, Rita, and Wilma) battered the Florida Keys during August–October 2005 (Lewis et al. 2009). Derelict lobster traps and trap-generated debris are detrimental to seagrass and coral habitats (Chiappone et al. 2005; Uhrin et al. 2005; Miller et al. 2008; Lewis et al. 2009). Significant declines in seagrass density occurred during prolonged deployment of lobster traps (6 weeks) in beds of Thalassia testudinum and Syringodium filiforme; after 6 months, the area directly beneath the traps had been denuded (Uhrin et al. 2005). Trap debris causes tissue abrasion in scleractinian corals, octocorals, and sponges (Chiappone et al. 2005; Miller et al. 2008), which contributes to loss of living habitat; the area affected is greater than a trap’s immediate footprint and can encompass several square meters when traps move during high winds (Uhrin et al. 2005; Lewis et al. 2009). During tropical storms and hurricanes a trap can move hundreds of meters from its site of deployment, possibly becoming repositioned in sensitive habitat not directly targeted by the fishery or an area in which fishing is prohibited (e.g., coral reefs, no-take areas). Areas of denuded substrate as large as 1.2 m2 were observed in a T. testudinum bed as a result of trap movement during Tropical Storm Gabrielle in 2001. Less than 2 months later, all traps in the same area had been lost following the passage of Hurricane Michelle (Uhrin et al. 2005). During Tropical Storm Barry in 2007, individual intact traps experimentally deployed on hardbottom habitat in 4 m of water moved an average of 23.06 m, resulting in an average affected area of 21.27 m2 per trap (Lewis et al. 2009). The affected area was largely denuded, and scleractinian corals, sponges, and gorgonians were sheared or detached (Lewis et al. 2009). Efforts to address the accumulation of derelict fishing gear have included debris recovery and programs designed to reduce overall fishing effort. The annual Trap Retrieval Program (TRP), initiated in the Florida Keys in 1985, is still underway. Shoreline and on-the-water cleanups recover lost gear primarily comprising polypropylene rope, polystyrene foam buoys, trap parts, and plastic trap throats (NOAA 2011); most on-the-water efforts target only those traps that are easily identifiable from the water’s surface (i.e., via surface buoys that are still attached). Each year 3,000–6,500 traps (spiny lobster and stone crab Menippe mercenaria combined) are retrieved from the waters of Monroe County in the Florida Keys (K. Miller, Florida Fish and Wildlife Conservation Commission, unpublished data). Excessive effort in the fishery (i.e., numbers of traps: Milon et al. 1999), which peaked at more than 900,000 traps in the early 1990s and was implicated in contributing to excessive mortality of sublegal-sized lobsters, declining trap yields, congestion and conflict on the water, and pollution, led to the implementation in 1993 of the Lobster Trap Certificate Program. Although annual trap reduction rates were established under this program, they have been amended over the years to include active reductions (10% of certificates held by each fisher are reverted back to the state) and passive reductions (up to 25% of certificates transferred in a sale from one fisher to another are reverted back to the state). The current 10% passive reduction rate has delayed progress toward meeting the existing trap reduction target of 400,000 established in 2005 (Florida Administrative Code R. 68B-24.009). Understanding the sources and processes that drive the spatial distribution of marine debris is crucial to remediation efforts (Martens and Huntington 2012). Previous efforts to characterize benthic marine debris in the Florida Keys National Marine Sanctuary were conducted in conjunction with studies of coral reef ecology and were confined to that habitat (Chiappone et al. 2002, 2004; Miller et al. 2008). Herein, we conducted marine debris surveys in the area primarily targeted by the commercial lobster fishery across all benthic habitats in the sanctuary (FWC and NOAA 2000; Matthews 2003; Sheridan et al. 2005). Basic information on the abundance and distribution of derelict lobster traps is required for evaluating the environmental impact of the spiny lobster fishery in the Florida Keys. Studies have measured either habitat degradation or lobster mortality due to confinement (Hunt et al. 1986; Uhrin et al. 2005; Lewis et al. 2009), but the magnitude of the problem could not be put into context fisherywide due to the lack of an estimate of the number of derelict traps. The objectives of this study were to (1) generate estimates of the abundance, composition, and spatial distribution of benthic marine debris in the sanctuary, with special regard to commercial trap debris, (2) describe habitatmediated patterns of debris accumulation, and (3) relate spatial D ow nl oa de d by [ C cf hr B ea uf or t L ab ] at 1 1: 09 0 2 Ju ne 2 01 4