Southern California Bight 2003 Regional Monitoring Program: IV. Demersal Fishes and Megabenthic Invertebrates
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- Results
- Natural Debris
- Anthropogenic Debris
- Discussion
IX. DebrisIntroductionMany studies have documented the types and amounts of marine debris that aesthetically impair coastal recreation areas and threaten marine organisms through ingestion and entanglement (Fowler 1987, Ryan 1987, Bjorndal et al. 1994, Moore et al. 2003). Several organizations have been and are currently collecting and analyzing debris data to inform the public of this growing worldwide problem (Ribic et al. 1997). Although marine debris is increasingly of concern, most studies have focused only on the types and amounts of large debris found on coastal beaches (MBC 1988, Ribic et al. 1997). In southern California, the Los Angeles Regional Water Quality Control Board has set a total maximum daily load of zero trash for several area watersheds based on the amounts of trash flowing from rivers and storm drains. However, few studies have documented the amount of trash that remains in the ocean versus that transported to beaches. A recent study (Moore et al. 2003) documented a density of eight pieces of plastic per cubic meter in the neuston while two regional studies conducted in 1994 and 1998 documented the types and amounts of benthic debris in the Southern California Bight (SCB) (Allen et al. 1998, Moore and Allen 2000, Allen et al. 2002a). This section presents the third regional study of debris on the seafloor of the SCB. The objectives of this section are 1) to assess the distribution, type, and amount of anthropogenic and natural marine debris on the seafloor of the mainland shelf of the SCB in 2003; and 2) to compare these findings to those of a 1994 regional baseline survey (Allen et al. 1998) and a 1998 regional survey of the southern California Bight (Allen et al. 2002a). ResultsDebris (natural and/or anthropogenic) was found in 122 of 210 (58%) trawl stations representing an area of 3,439 km2 (39% of the area) on the southern California shelf and upper slope. Natural debris occurred in 40% of the area of the shelf and upper slope, whereas anthropogenic debris occurred in 25% of the area (Table IX-1). Anthropogenic debris was primarily found off of highly populated areas while natural debris was typically found in the southern region (Figure IX-1). Natural DebrisNatural debris varied in areal coverage by subpopulation (Figures IX-2 and IX-3). Regionally, the percent of areal coverage of natural debris increased from the northern (30%) and central (41%) to southern (76%) regions (Table IX-1). The areal coverage for island subpopulations showed a similar pattern where the percent of areal coverage of natural debris increased from the cool northwest channel islands (13%) to warm southeast channel islands (23%). Bathymetrically, natural debris had the highest percent of area on the inner shelf (53%), followed by bays and harbors (50%), upper slope (40%), middle shelf (37%), and outer shelf (26%). Within the middle shelf, small POTWs had the highest percent of area of natural debris (92%) followed by non-POTW (46%), large POTWs (40%), and the islands (21%; Figure IX-3; Table IX-1). Inner shelf natural debris occurred in the highest percent of area in the large and small POTWs (100%), followed by the mainland (52%). On the outer shelf, the percent of area of natural debris was highest in the mainland area (37%) and lowest in the large POTWs (0%) and island (0%) areas. The percent of area for natural debris in the upper slope was highest in the mainland (40%) area and lowest in the island (0%) area. On the mainland shelf of southern California, marine vegetation was the most commonly occurring natural debris, followed by terrestrial vegetation, rocks, and benthic debris (Table IX-1). Natural debris was most commonly found in trace numerical densities (one item per haul) and trace weight densities (0.0-0.1 kg; Table IX-2). Different types of natural debris also varied by subpopulation (Table IX-1). Marine vegetation was most widely distributed in inner shelf small POTWs (53%) and least distributed in the outer shelf large POTWs and outer shelf and upper slope island areas (0%). Terrestrial vegetation occurred most commonly in large POTWs (33%) and was absent in island areas, inner shelf small POTW and mainland areas, and outer shelf large POTWs areas. Benthic debris was the least common type of natural debris in the SCB with the highest areal coverage found in the outer shelf mainland and middle shelf island areas (8%). Rocks were also uncommon on the soft bottom of the SCB, with the highest areal coverage occurring in outer shelf mainland (29%) areas. Anthropogenic DebrisAnthropogenic debris also varied by subpopulation (Figures IX-2 and IX-3). Regionally, inner shelf large and small POTWs (100%) had the highest areal coverage of anthropogenic debris and the outer shelf POTWs and outer shelf and upper slope island areas the lowest (0%; Table IX-1). Along the mainland, anthropogenic debris had the highest aerial coverage in the central (50%) region followed by the southern (28%) and northern (17%) regions. Unlike in previous surveys, anthropogenic debris was not found at the Channel Islands. Bathymetrically, anthropogenic debris occurred most commonly in the outer shelf (35%), followed by the upper slope (32%), bays and harbors (31%), middle shelf (25%) and inner shelf (1%) zones. The only occurrence (33%) of anthropogenic debris on the inner shelf occurred at large POTWs. On the middle shelf, non-POTW areas had the highest areal coverage (39%) of anthropogenic debris, whereas middle shelf small POTWs had the least (8%). On the outer shelf, mainland areas had the highest occurrence (50%) and large POTWs and island areas the least (0%). Anthropogenic debris consisted of cans, glass bottles, fishing gear, metal, paper, plastic, lumber, tires, and “other” debris. On the mainland shelf of the SCB, plastic occurred most commonly and paper the least. Anthropogenic debris occurred primarily at trace abundance and weights (Table IX-2). However, metal and fishing gear occurred most commonly at low numerical densities and metal and glass bottles at low weight densities. Anthropogenic debris types were found to vary by location and subpopulation along the southern California shelf (Figure VI-4, Table IX-1). Regionally, all types of anthropogenic debris occurred in the central region, with plastic occurring most commonly (28%) and paper the least (1%). In the southern region, “other”, fishing gear, metal, and plastic occurred most commonly (10%, 9%, 9%, and 5% respectively) and all other types of anthropogenic debris were absent. In the northern region only plastic, lumber, and cans were present (9%, 8%, and 1% respectively). Cans were the only form of anthropogenic debris found on the inner shelf and only in large POTWs areas. On the middle shelf, plastic occurred with equal frequency in large POTWs (12%) and non-POTW (12%) areas. Plastic, cans, metal, tires, and “other” debris occurred nearly equally in both middle shelf large POTW and non-POTW subpopulations; fishing gear and glass bottles occurred only in middle shelf non-POTW subpopulations (Figure IX-5). On the outer shelf, metal (21%) and cans (13%) occurred most commonly on the mainland shelf (Table IX-1). On the upper slope plastic (20%) and lumber (12%) and “other” (8%) debris were the only anthropogenic debris that occurred and were found only in mainland areas. DiscussionAnthropogenic and natural debris were found throughout the mainland shelf of southern California (Figure IX-1), generally in trace amounts. Anthropogenic debris was highest in the central region due to the proximity of large populations to these areas (near Los Angeles metropolitan areas). Anthropogenic debris was found in similar numbers for all shelf zones (about 30%) except for the inner shelf zone (1%). The high occurrence of anthropogenic debris in bays and harbors is likely from land-based and marine vessel sources. The next highest occurrence of anthropogenic debris on the middle shelf, outer shelf, and upper slope is likely from a combination of recreational fishing and boating sources, and from historical runoff events. The lack of anthropogenic debris in the inner shelf may be due to wave and tide transport of sand and debris downcoast to submarine canyons and the lack of recent storms prior to the 2003 survey season (Table IX-3). Plastic was the most commonly occurring debris item in all subpopulations, except for the outer shelf island areas, where metal and cans were the most common. Terrestrial debris, a component of natural debris and a potential indicator for the path of anthropogenic debris from land-based sources, increased in areal extent from north to south. Bathymetrically, terrestrial debris was most common in the deeper waters of the upper slope, followed by the middle and outer shelf zones, and while it occurred in bays and harbors, it was almost absent in the inner shelf. The lack of terrestrial debris on the inner shelf was similar to that of anthropogenic debris and may be due to the lack of wave and tide action and lack of recent storms as well. On the middle shelf, terrestrial debris was most common in small POTW areas followed by non-POTW areas, and finally large POTW areas. Terrestrial debris, similar to anthropogenic debris, was absent in island areas which are narrower compared to those on the mainland. The present study (2003) was part of the third region-wide monitoring effort of the SCB. The first study, in 1994 (Allen et al. 1998, Moore and Allen 2000), provided a baseline for comparing the amounts of debris to those found in 1998 and 2003. In 1994 about 14% of the SCB had anthropogenic debris, whereas in 1998 this number increased to 23%, and in 2003 was about the same at 25%. This is largely due to the fact that more extensive surveys were done in 1998 and 2003 (314 stations in 1998 and 210 in 2003 compared to 114 for 1994) and to the inclusion of bays, harbors, and islands. Trends for all three (1994, 1998, and 2003) studies were similar in that most of the debris occurred in small amounts and small biomass; however, trends for occurrence varied. The higher occurrence of anthropogenic debris in the central and southern regions (the most populated) was similar to that found in 1994 and 1998 (Figure IX-6). For 1994 and 1998, plastic, metal debris, and glass bottles occurred over a much larger area at large POTW areas and were thought to be most likely from recreational boat uses; however, in 2003 most items were distributed evenly among the large POTW areas with the exception of fishing gear and glass bottles which were found only in non-POTW areas (Figure IX-7). Overall, anthropogenic debris had higher areal extent in all subpopulations for 2003 versus the previous surveys, with the exception of the inner shelf and POTW subpopulations. This higher areal coverage in 2003 is thought to be due to boating and shipping activities as well as to debris left by historical runoff events. Terrestrial debris had higher areal extent in the northern region for the 1994 and 1998 surveys but was higher in the southern region for the 2003 survey (Figure IX-8). The higher areal extent in the northern region for the previous surveys was thought to be due to large rain events prior to the surveys (Table IX-3). In 2003 no such rain events occurred, and the rain for this season was not only less but the previous year was a drought year. Overall, terrestrial debris occurred over less of the area in all subpopulations in 2003 versus 1994 and 1998, with the exception of the southern region. In conclusion, while anthropogenic debris occurred in about 25% of the SCB, it was not present in large quantities. Anthropogenic debris had higher areal coverage for this survey compared to previous surveys, whereas terrestrial debris had less coverage, suggesting a possible relationship to seasonal rain totals. As marine debris becomes of greater concern to the public, not only for aesthetic reasons, but also in regard to marine organism health, regional monitoring studies such as this one, done at regular intervals, will provide valuable information on the types, amounts, and location of debris in the marine benthic habitat. Hence, it is recommended that this survey be continued as part of future regional surveys of the SCB. Table Table IX-1. Percent of area by subpopulation of debris types on the southern California shelf and upper slope at depths of 2-476 m, July-October 2003. 
Figure IX-1. Distribution of natural and anthropogenic debris on the mainland shelf and upper slope of southern California at depths of 2-476 m, July-October 2003. 
Figure IX-2. Percent of area with natural and anthropogenic debris by region and depth on the southern California shelf and upper slope at depths of 2-476 m, July-October 2003. 
Figure IX-3. Percent of area with natural and anthropogenic debris by subpopulation within shelf zones on the southern California shelf and upper slope at depths of 2-476 m, July-October 2003. Table Table IX-2. Percent of area of quantification categories of debris types collected on the southern California shelf and upper slope at depths of 2-476 m, July-October 2003. 
Figure IX-4. Distribution of anthropogenic debris types on the southern California shelf at depths of 2-476 m, July-October 2003. 
Figure IX-5. Percent of area of anthropogenic debris types on the mainland middle shelf (31-120 m) in publicly owned treatment work (POTW) and non-POTW subpopulations of southern California, July-October 2003. 
Figure IX-6. Percent of area with anthropogenic debris by year and subpopulation within regions, depths, and large POTW areas on the southern California shelf and upper slope at depths of 2-476 m, July-October 2003. 
Figure IX-7. Percent of area of anthropogenic debris categories in large publicly owned treatment work (LPOTW) and non-LPOTW subpopulations on the mainland middle shelf (31-120 m) of southern California in 1994, 1998 and 2003. NOTE: 1994 data has been reclassified into 1998 and 2003 subpopulations and hence may differ from Allen et al. (1998) and Moore and Allen (2000). 
Figure IX-8. Percent of area with terrestrial debris by year and subpopulation within regions, depths, and large POTW areas on the southern California shelf and upper slope at depths of 2-476 m, July-October 2003. Table Table IX-3. Total seasonal rainfall (precipitation) for Los Angeles Civic Center for year before and year of regional surveys (Taken from the Los Angeles Almanac (www.laalmanac.com/weather)). 
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