HANAN ET AL.: SEA LIONS AND COMMERCIAL PASSENGER FISHING VESSELS CalCOFl Rep., Vol. 30,1989 CALIFORNIA SEA LION INTERACTION AND DEPREDATION RATES WITH THE COMMERCIAL PASSENGER FISHING VESSEL FLEET NEAR SAN DIEGO DOYLE A. HANAN, LISA M. JONES ROBERT B. READ California Department of Fish and Game California Department of Fish and Game c/o Southwest Fisheries Center 1350 Front Street, Room 2006 P.O. Box 271 San Diego, California 92101 La Jolla, California 92038 ABSTRACT anchovies, Engraulis movdax, which are thrown California sea lions depredate sport fish caught from the fishing boat to lure surface and mid-depth by anglers aboard commercial passenger fishing fish within casting range. Although depredation be- vessels. During a statewide survey in 1978, San havior has not been observed along the California Diego County was identified as the area with the coast among other marine mammals, it has become highest rates of interaction and depredation by sea a serious problem with sea lions, and is less serious lions. Subsequently, the California Department of with harbor seals. The behavior is generally not Fish and Game began monitoring the rates and con- appreciated by the boat operators or the anglers, ducting research on reducing them. The sea lion even though some crew and anglers encourage it by interaction and depredation rates for San Diego hand-feeding the sea lions. County declined from 1984 to 1988. During depredation, sea lions usually surface some distance from the boat, dive to swim under RESUMEN the boat, take a fish, and then reappear a safe dis- Los leones marinos en California depredan peces tance away to eat the fish, tear it apart, or just throw colectados por pescadores a bordo de embarca- it around on the surface of the water. The angler or ciones pesqueras deportivas. La investigacih lle- observer may never see the sea lion take a fish off vada a cab0 en el estado de California en el afio 1978, the hook. What the angler experiences after hook- identific6 a1 condado de San Diego como el Area con ing a fish and starting to reel it in is a tremendous la tasa de interacci6n y depredacih mAs alta. En tug and rush of line as the sea lion takes the fish. consecuencia, el departamento “California Depart- Occasionally, the sea lion itself may get hooked and ment of Fish and Game” inici6 un programa de get away by breaking the line, but it then carries the monitoreo de las tasas y condujo una investigacih fishing hook until the hook rusts away. con el objeto de reducirlas. Los valores de las tasas In 1978, the California Department of Fish and de interaccih y depredacih del leon marino en el Game (CDFG) began studying sea lion-fisheries in- condado de San Diego declinaron desde 1984 a 1988. teractions, and determined that the fishery off San Diego County was one of the most adversely af- INTRO D U CTI 0 N fected in the state (Miller et al. 1983). The adverse California’s largest commercial passenger fishing effects included interactions (presence near a fishing vessel (CPFV) fleet operates from San Diego vessel) and depredations. Since that time, CDFG County with boats ranging in size to about 100 feet. biologists have investigated methods of reducing The boats make scheduled trips for various lengths the interaction and depredations. Additionally, of time: half-day, three-quarter-day, full-day, they have continued to monitor the rates while multi-day, and twilight or evening. Passengers pay aboard the vessels to identify and measure the fish a fee to ride these boats and catch, with rod and reel, caught. a variety of fish species, depending on the trip Some methods that have been tried for reducing length, season, and fish availability. or eliminating the interactions are small explosives, California sea lions, Zalophus califovnianus, and rockets, noise emitted through underwater trans- occasionally Pacific harbor seals, Phoca vitulina vi- ducers, slingshots, guns, and chemical deterrents. chavdsi, swim near or follow these boats and may An additional method of stopping troublesome sea take (depredate) the fish that have been caught and lions from bothering a particular fishing vessel was are being reeled in. In addition to taking the angler’s to move the boat to a new area and, while moving, catch, these marine mammals eat the fish used for pass close enough to another fishing boat so the sea chum. Chumming is done mainly with northern lion becomes interested in the second vessel’s oper- ation and “drops or passes off’ on it. Each method [Manuscript received February 1,1989.1 has limitations, and none works in every case or 122 HANAN ET AL.: SEA LIONS AND COMMERCIAL PASSENGER FISHINGVESSELS CalCOFl Rep., Vol. 30,1989 against individual sea lions that repeatedly depre- date catch (Scholl 1987; Scholl and Hanan 1987a, 1987b). SAN DIEGO COUNTY In 1986, despite negative findings about the effec- tiveness of nonlethal deterrents, the Sportfishing 200 Imperld Beach FISHING SPOTS 200 811~~SIrmdlCoronado Association of California (an organization of CPFV 212 0.11 Rocelver operators) applied for and received a general permit from the National Marine Fisheries Service allow- ing CPFV operators to obtain certificates of inclu- sion. The certificates gave the operators permission 229 Ball Recelver to use nonlethal methods of harassment to keep sea 230 Neamhore MI88lOn Bay 233 Olfahore MIsslon Bay lions away from their fishing activities. Recently a 236 P.cIIIc Beach number of CPFV operators have stated that they 239 N. La Jolla have stopped using the deterrents. 241 La Jolla Cove 247 Scrlpp~PlerlTorfey Plnsa Clllll) Sea lion interaction and depredation rates are 254 Torrey Pln.8 Slate Beach summarized and analyzed for the San Diego 255 Del MarIRaCe Track 267 Del Mar N. County CPFV fleet during the 1984-88 period to 268 San Elllo La~oonInBhore determine trends in those rates. 201 5.n Elllo Lagoon Oftahore 283 Cardill-by-the-Sea 288 ~nciniiaa MATERIALS AND METHODS 208 ~.tiqultoa Laooon Field data were gathered by CDFG observers 273 Edna Power Plant aboard CPFVs to investigate deterrents or to iden- 278 Bait Receiver tify and measure the fish catch. .For this study, we 278 Ollahore Oceanside Harbor used only information from half-day, three- 280 .New’ Ocsanslde ArtIIldaI Reel 282 .Wreck’ICamp Psndleton quarter-day, and twilight trips, which limits this 283 Barn K0lplCsmp Pendleton study to fishing areas near the mainland and does 280 YeII~wtaiIKelp1 Camp Psndleton 281 Sa” onotre Power Plant not include any trips to the offshore islands, where sea lion interactions and depredations are reported to occur more frequently. Because harbor seals Figure 1. San Diego fishing spots used by commercial passenger fishing vessels (partyboats) are divided into three complexes depending on home were rarely involved, they are not included in the port of the vessels using the fishing spots. summaries or analyses. The specific boats and the types of trips observed were chosen randomly, but space availability and crew cooperation played a hooked (this implies that it ate a fish). The observer part in the selection. counted one sea lion taking multiple fish as a single Observers completed specially developed data depredation. Eating the chum or being hand-fed forms when they saw a marine mammal interaction was not considered depredation. or depredation. The forms included port oflanding, CPFVs often made several fishing stops during a fishing area by complex (figure l), Fish and Game trip; when sea lions appeared at more than one stop, boat identification number, boat name, date, name the observer was asked to determine whether they of stop (fishing spot), number of marine mammals were the same animals at each stop. Skippers often involved, number of marine mammals taking fish, attempted to “pass off’ sea lions that were follow- kind of fish taken, the length of time spent at the ing them. If the technique was unsuccessful, a single stop, total time for the trip, and whether the same sea lion could have several interactions or depreda- mammals followed the boat and appeared at each tions involving a particular fishing vessel during fishing stop. one fishing trip. Each interaction or depredation We defined an interaction as a sea lion swimming was recorded as a separate incident for the summary within 100 yards of the boat, because some boat and analysis. operators claim that the mere presence of a sea lion Field data were entered into a microcomputer will “shut down the bite” (discourage fish from data base for summary and analysis. The data were feeding and often scare them away from the boat). grouped by area into three overlapping regions (re- A depredation was defined as a sea lion taking one ferred to as complexes by the CDFG project that or more hooked fish (including part of a fish, since samples these fishing vessels) based on home port sea lions will often take the body and leave just the of the CPFV: San Diego Bay (Pacific Beach, Point fish head on the hook) or a sea lion itself becoming Loma, and Imperial Beach); Mission Bay (La Jolla, 123 HANAN ET AL.: SEA LIONS AND COMMERCIAL PASSENGER FISHING VESSELS CalCOFl Rep.,Vol. 30,1989 1984 1985 1986 1987 1988 1984 1985 1986 1987 1988 2.4 I 0' I I I I I I - 8.4 0 2.0 - 0 $ 2.01 Q 0 Months Figure 2. Average number of sea lions interacting (within 100 yards of the boat) per trip sampled with commercial passenger fishing vessels plotted by month, 1984 through 1988 (open circles), fit with a three-month running mean (solid line) and polynomial regression (broken line). - om 0.0.