Investigation of Tagging Methods and Tracking for Giant Pacific Octopus (Enteroctopus Dofleini) in Southcentral Alaska

Final Report Investigation of tagging methods And tracking for Giant Pacific Octopus (Enteroctopus dofleini) in Southcentral Alaska Alaska Fisheries Development Foundation Principal Investigators: Patrick Barry, Reid Brewer, James Browning, Jamie Grund, David Scheel, David Tallmon and Sherry Tamone Award Number: COBS: NA04NMF4540379 Report Period: 7/01/2004 – 12/31/2006 Prepared: 3/25/2007 Compiled by: James Browning – Deputy Director Alaska Fisheries Development Foundation Introduction: The giant Pacific octopus Enteroctopus dofleini (Wülker 1910), is a charismatic mollusk that is fished throughout its range from Baja California to the Aleutian chain in Alaska and westward in the North Pacific to Japan. Octopuses, like squid, are cephalopods that collectively contribute to a 2.5 million ton harvest in worldwide fisheries (Rocha and Vega, 2003). There is interest in developing the commercial harvest of E. dofleini in Alaska to serve overseas food markets and for use as bait in other Alaskan fisheries. The general life history of the giant Pacific octopus includes a very short life span (3-5 years) with mating occurring in the late fall and winter, followed by the death of the adults prior to egg hatch. (Hartwick, 1984). The high growth rates and fecundities of this species are life history traits that could contribute to the potential success of an octopus fishery. What little is known about the potential fishery of this species and population dynamics was detailed in a previous report (Paust 1988). There is an obvious management need to explore methods that estimate their abundance and distribution in regions of Alaska that could sustain a fishery. The lack of an adequate stock assessment, the main obstacle in developing an octopus fishery (Conners and Jorgensen, 2005), has stunted the growth of a profitable market in Alaska. Much of the research on E. dofleini focuses on feeding preference (Hartwick et al., 1981), habitat use (Hartwick et al., 1984; Scheel, 2002), and development (Gabe, 1975; Hartwick, 1983). Spawning occurs throughout the year, but is most prevalent in winter (Hartwick, 1983). Approximately 42 days after copulation (Gabe, 1975), females lay 18,000 -100,000 eggs over a period of several days (Hartwick, 1983). Incubation takes 150 days to 7 months depending on the water temperature. The female tends to the eggs; cleaning and aerating them, but does not feed during this period. After the eggs hatch, the female dies. Recently hatched young, 3-4mm dorsal mantle length, spend 2-3 months in the plankton (Kanamaru and Yamashita, 1967). After reaching 3-5 g they settle out of the plankton and begin their benthic existence. Most commonly found in intertidal and shallow subtidal areas (Scheel, 2002), some octopuses have been caught at depths of 750 m (Paust, 1989). Considered a refuge predator, E. dofleini inhabits naturally occurring dens (under rocks, in crevices, or excavated sand and gravel under boulders) as well as refuse. In Japan E. dofleini makes two onshore/offshore migrations annually, however, no such migrations have been observed in the Eastern Pacific. Off the coast of British Colombia, immigration rates peaked in July/August and November/December, but monthly departure rates were highly variable and could not be distinguished from random (Hartwick et al., 1984). Over a two week period, Mather (1985) observed that E. dofleini exhibit small overlapping home ranges (250m2 maximum). Hartwick (1984) observed some seasonal pattern of movement where individuals would leave for up to 177 days and return, but attributed this behavior to the octopuses’ memory of prey distribution and foraging success. Success in the octopus fishery may therefore be determined by local knowledge of indicator species as Paust (1988) suggests. Mark-recapture methods are used in fisheries and wildlife management practices to estimate population abundances. To that end, we explored the use of different capture and marking methods in Kachemak Bay and Prince William Sound, Alaska. Octopuses are soft bodied and we compared the Peterson disc tag, which is a piercing tagging method and has been employed in earlier studies (Scheel et al, 2002), as well as injectable elastomer visible tags that have been used with success on other cephalopod species (Replinger and Wood, 2006). Whereas mark and recapture techniques may be of limited use in the assessment of population abundance estimates in the absence of sufficient recaptures, the comparison of tagging methods will be useful in establishing the most efficient protocols. Additionally, all recaptures can generate some information concerning growth and movement of individual animals, information that is severely lacking in wild populations of GPO. Understanding the demographic and evolutionary relationships among natural populations is also critical to sound management (Waples 1998). If populations share large numbers of migrants and contain little unique genetic variability, then it is possible to manage them as a single unit. Harvest from one area will not lead to the loss of a unique stock or deplete genetic variation necessary to adapt to a changing environment. However, if populations share few migrants and are genetically unique, then it is important to manage them as separate units. In this case, individual populations must be managed as separate stocks to avoid local depletion events. We will use DNA techniques to establish the genetic population structure and evolutionary relationships of E. dolfleini populations in Alaska. No microsatellite primer sequences are published for E. dofleini, however, homologous loci are likely to be amplified in related species using the same primers (Murphy et al, 2002, Jarne and Lagoda, 1996; Schlotterer et al., 1991). While no comprehensive study of E. dofleini population structure exists, sequencing of the COIII region by Sosa et al. (1995) and microsatellite primers for O. vulgaris developed by Greatorex et al. (2000) make such a study possible. Objectives: The primary objectives of this project were to 1) assess the relative abundance and growth rates of the giant Pacific octopus in Prince William Sound and Cook Inlet . 2) examine the catch rates for octopus using different gear types. 3) compare two different methods to mark individuals. 4) initiate a genetic analysis of this species to better understand the demographic relationships among Alaskan octopus populations. 5) Investigate movement parameters of GPO w/ sonic tags. Tagging: Modified Peterson disc vs. injected Elastomer Materials and Methods: Animal Sampling: We sampled octopuses in Kachemak Bay and Prince William Sound, Alaska. Designated a national estuarine research reserve in 1999, Kachemak Bay is an extremely diverse and productive system. Prince William Sound is surrounded on three sides by the Chugach Mountains, while an array of islands protect it from the Gulf of Alaska. These sites were selected because they were thought to be prime candidates for an octopus fishery (Carroll personal communication). Sampling Dates. Three sampling sessions were completed and included the first charter 5/29/06 to 6/18/06, the second charter 10/2/06 to 10/13/06 and the third charter11/25/06 to 12/6/06 using contracted vessels (F/V Shady Lady, Chignik, Alaska for the first and third charters and F/V Centurion, Homer Alaska for the second charter). Gear Type: Four different types of pots were used during the course of the study, including Korean hair crab pots (45cm tall, 100cm base diameter with a 26cm plastic tunnel), lair pots (60.96cm x 30.48cm x 30.48cm with a 15.42cm x 30.48cm opening), both commercial and personal use Ladner shrimp pots (7.62cm tunnel openings on both), and black cod pots (147 cm steel frame, 122 cm bottom ring, 71 cm top ring, 76 cm ht, with 25 cm sock tunnel and 7 cm black seine net). All pots except the lair pots were baited using shredded herring in bait canisters. Shrimp pots were baited with either herring or prawn pellets. During the first sampling session we used a total of 50 Korean hair crab pots and 50 lair pots, set in strings of 10 pots of each type. Pots were spaced 9 m apart and marker buoys were attached to both ends of each string. We left the Korean hair crab pots to soak for an average of 64.8 (±0.64 SE) hours, while the lair pots soaked for 155 (±3.59 SE) hours. We set the Korean hair crab pots at an average depth of 90.9 (± 1.82 SE) m, targeting Tanner crab, Chionoecetes bairdi. Lair pots were set on muddy bottoms at an average depth of 75.3 (±3.18 SE) m, where clam and scallops were most abundant. Because of the poor capture success during the first sampling effort, we focused all subsequent sampling efforts in Kachemak Bay and added shrimp and black cod pots to our second sampling event. With higher catch rates during the second and third session, lengthy handling time for individual octopus resulted in increased soak times for all gear types. Black cod, Korean hair crab, Lair, and shrimp pots soaked for 103 (± 2.04 SE) hours, 66.5 (±1.77 SE) hours, 200 (± 3.70 SE) hours and 96.1 (±3.26 SE) hours respectively. The number of pots on each string was increased to 20 (except for lair pots which increased to 16), with the pots again separated by 9 m. Pot depths varied for all pot types in an attempt to maximize their efficiency. Average pot depth for all three surveys was 94.9 (±0.55 SE) m for black cod, 90.7 (±1.19 SE) m for Korean hair crab, 86.8 (±1.20 SE) m for lair, and 96.1 (±3.26 SE) m for shrimp pots. Each string of pots consisted of a single pot type to make the process of pulling/setting as safe as possible. In our final sampling efforts, we removed both types of shrimp pots from the sampling design because of their low CPUE.

Load more