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Aspects of the Ecology of the Red Squid (Ommastrephes bartramii), a Potential Target for a Major Hawaiian FisheryProgress Reports (PDF): FY 2002, FY 2001, FY 2000, FY 1999, FY 1998 (see below), FY 1997
This project examines the general ecology of the red squid Ommastrephes bartramii in the central North Pacific near the Hawaiian Archipelago. Our interest in the red squid is based on (1) its considerable potential for a Hawaii-based commercial fishery and (2) its importance in the ecology of the broadbill swordfish which is a major commercial fishery in Hawaii. This project involves strong cooperative aspects with the National Marine Fisheries Service (NMFS), Honolulu Lab and Hokkaido University in Japan.
In order to study this squid, we must have effective sampling methods. For catching adult squid, we have experimented with large trawls, pole and line jigging, automatic jigging machines and squid driftlines. None of the methods have been satisfactory as yet. The squid driftlines, however, seem to have the greatest potential. At present, most of our sampling is done aboard the FTS HOKUSEI MARU from Hokkaido University although we have samples from commercial fishermen and NMFS. For sampling paralarvae we used standard plankton nets aboard the HOKUSEI MARU.
At present we are trying to obtain data on latitudinal trends in feeding, reproductive condition and abundance. Our data, although meager, suggest that squid are most abundant in the vicinity of the subtropical front. Unlike males, females are difficult to capture south of the front, and we suspect this is due to a deeper nighttime habitat in these warmer waters which would make females less vulnerable to our sampling gear.
Paralarvae are caught predominantly south of the front but are very patchy and widely scattered there. Apparently the spawning grounds of this squid constitute a broad area south of the subtropical front. In the Hawaiian region, the squid feed predominately on midwater fishes and other squids. There is some indication that supplemental feeding occurs during the daytime in deep water and that food is more abundant near the subtropical front. Our present evidence suggests that the red squid is a multiple spawner and that spawning is fueled by feeding on the spawning grounds.
Dr. Richard Young
Department of Oceanography
University of Hawaii at Manoa
1000 Pope Road, MSB 631/634
Honolulu, Hawaii 96822
Phone (808) 956-7024
FAX (808) 956-9516
Department of Oceanography
University of Hawaii at Manoa
1000 Pope Road, MSB 614
Honolulu, Hawaii 96822
Ph. (808) 956-6775/7632 (lab)
FAX (808) 956-9516
FY 1998 Progress Report (year 2)
Richard E. Young and Jed Hirota
(Note: Please contact project investigators for figures)
IntroductionOur February cruise departed with bad weather conditions north of the main Hawaiian Islands that indicated we would probably be unable to get north of Kauai. As a result our cruise plan, which was to run west to 165° W, and then turn north was abandoned. Instead we attempted to work straight north in case we had to retreat to the lee of the high islands. We were lucky, however, and were forced to run south on only one occasion (Fig. 1). Marginal weather conditions and a full moon appearing in the middle of the cruise resulted in poorer catches than in the previous two years.
Gear developmentOn the assumption that the female red squid were in deeper water south of the subtropical front, we set vertical squid drift lines at four stations and our regular horizontal drift lines at seven stations. The vertical sets varied between 2-7 lures per line spaced at 20m intervals to a maximum of 190 m of line out. None of the vertical sets resulted in any red squid catches. Hooks on a vertical drift line may have been too deep for the squid attraction-lights aboard the ship to be of much value and the lighted jigs and glo-sticks that we used produce only a very small amount of light. Whether or not this is the cause of our poor catches is uncertain. The Japanese, however, on the summer jigging grounds have used bright attraction-lights, powered from the ship, that are lowered to depths of several hundred meters to successfully fish for squid during the daytime. Unfortunately we do not have the gear capability to try this approach.
The horizontal drift lines caught red squid only at the two northern-most stations where three males were caught on each set.
Distribution of adult male and female red squidAs usual the 1998 catch of males was much larger than the catch of females. A total of 64 males and two females were captured (Fig. 2). In 1997 we noted that the average size of male red squid was longer than in the previous year. In 1998 the sizes were smaller and comparable to sizes seen in 1996 (Fig. 3). A size differential in females was also noted between 1996 and 1997. The small number of females captured in 1998 could not indicate size distribution for that year (Fig. 4). The distribution of the male red squid was peculiar during our 1998 cruise (fig. 5). No squids were captured until we reached 28° N lat. but good captures were made on the return trip through some of the same waters. Unfavorable moonlight conditions probably contributed to the problem on the first part of the cruise. The two females captured were taken at or near the s ubtropical front (Fig. 6). The capture of females near the subtropical front has become a fairly consistent pattern over our three cruises. NMFS cruises in May show a similar trend relative to the front. In contrast to the previous two cruises, we found no latitudinal trend in the size of males with latitude (Fig. 7). We suspect that this is simply a reflection of insufficient number of squid taken at the extreme geographical ends of our sampling area.
Distribution of paralarvae
Due to rather low catches of paralarvae during the previous two cruises, we altered our sampling regime in 1998. Instead of taking three oblique tows from 0-25m, we took two such tows and one horizontal tow at the surface at each station. When paralarvae were abundant the surface tow captured far more paralarvae than did the oblique tows although when converted to catch per unit area, the oblique tows out-preformed the surface tows. When paralarvae were in low abundance, the absolute catch of the two methods was about the same. The distribution of red squid paralarvae, as seen by the oblique tows, was consistent with that of previous years (Fig. 8). Paralarvae were absent near and north the subtropical front, as determined by the position of the 19° C surface isotherm, but were consistently found well to the south of it. This data combined with our previous work on this species (Bower, 1995), indicates that the red squid spawns preferentially where surface water temperatures are between 21 and 24° C. Although adult females are mostly captured near the subtropical front, the presence of paralarvae well south of the front indicates that females must be there as well. Apparently, on the spawning grounds, the behavior of the female squid changes. Females may occupy deeper water at night and are not being brought to the surface by our attraction lights.
FeedingInitial processing of 248 O. bartramii stomachs has been completed for the three cruises. Stomach contents were analyzed to determine if preferred areas for feeding exist and to determine dominant prey items. Wet weights of stomach do not yield any apparent trends when compared to distance from the subtropical front which is presumably a better feeding area (Fig. 9). To eliminate possible abnormal feeding under the influence of the ship's lights prior to capture, stomachs containing fresh material (nearly undigested) were excluded (Fig. 10). Even with the removal of this bias, the data still lack any clear trends.
Squid stomach data, in general, and especially where squid must be caught via attraction to food, contains a lot of variability and trends are not easily detected. One method for finding trends is to use the otoliths and eye lenses found in the stomach as a proxy of stomach fullness. In the case of the red squid, the number of fish eaten, as estimated by otoliths and lenses, seem to increase near and north of the subtropical front (Fig. 11). This trend seems more apparent when viewed within an individual year than when the data are taken as a whole (Fig. 11). On average the number of otoliths found in stomachs was 2.15 times greater than the number of lenses. Perhaps eye lenses pass through the digestive system of the squid faster than the otoliths, if so, the otoliths represent a longer feeding history while the lenses depict a more recent feeding regime. The trend observed is apparent only with the otolith data.
Although feeding with respect to distance from the subtropical front shows a great deal of variability, gross feeding preference seems to remain relatively constant from year to year. Otoliths were present in 92% of all stomachs analyzed, including empty stomachs, while squid beaks were present in 51% of stomachs. These percentages were held fairly constant between years (Fig. 12). Work is ongoing to identify the otoliths down to the family level in most cases and down to genus or species level within the family Myctophidae because of its importance as prey to the red squid. Although the final results are not yet complete Matt Parry gives initial estimates that roughly 70% of the otoliths present in O. bartramii stomachs belong to members of Myctophidae.
Matt will present the results to date of the feeding studies at the I.C.E.S. meeting in Portugal in September of this year.
ReproductionWith the capture of only two mature female red squid during the 1998 cruise we are able to add little to previous data. The relationship of the nidamental gland weight plotted against the oviduct weight (oviduct weight is mostly due to the presence of mature eggs) falls in the same trend as seen previously (Fig. 12). This trend suggests that examining the histology of the nidamental glands may provide evidence for multiple spawning. This is something we will attempt to accomplish this fall.
Coordination with related programsWe maintain close working relationships with NMFS, especially with Mike Seki. As in the past Mike has provided us with frozen stomachs from most squid taken during his cruise as well as a few frozen females.
Request for Supplemental FundingOur project was funded for two years although the project technically extends for five years. We wish to continue studying the red squid, however, for the full five years. We have an agreement with Hokkaido University to have their ship HOKUSEI MARU available for this period and we have submitted a proposal to International Programs at NSF to fund the annual cruises for the years 2000 and 2001. However due to the long lead time required for the proposal process, we were unable to apply for support for the year 1999. We request that the PFRP support the cruise during that year. One major expense is the cost for food for U.S. participants. Unlike U.S. ships in the academic fleet, Japanese ship-regulations require foreign participants to pay for their meals.
To date, the research has been valuable but we have been disappointed by any major improvements in our ability to catch the red squid. In addition, our Japanese colleagues seem to have lost interest in trying innovative fishing approaches. Without considerable capitol investment in equipment, we now expect that any progress in this area will be minimal. Our interest in continuing the project rests in our desire to better understand the reproductive and trophic ecology of this important squid. The reproductive ecology aims at determining whether or not the red squid is a multiple spawner and how frequently it spawns. We require more data and further work on the histology of the nidamental glands and examination of statoliths to solve these problems. With regard to the trophic ecology, we have made considerable progress in understanding the prey composition of the red squid diet, but more work needs to be done in identifying prey to the genus and species levels. The aspect of trophic ecology, however, that has us most excited, is the prospect of using stable isotopes to better understand the trophic position of the squid and to trace its migrations and trophic status over time through the analysis of secreted structures (gladius, beaks, eye lenses). In addition, other tissues that have varying metabolic rates should provide average isotope values commensurate with the turnover time of the tissue. Some tissues, therefore, will reflect the immediate feeding history (e.g., blood, ink) while others will integrate the feeding history over longer time spans (e.g., mantle muscle). SOEST now has a state-of-the-art Isotope Biogeochemistry Laboratory (run by Brian Popp) in the POST building. This is an automated system run by a technician and charges are $10/sample. There are many factors that cause variations in stable isotope ratios (e.g., tissue turnover times, variation in values at initial trophic levels due to a variety of effects such as temperature) and when carefully evaluated, this "variability" can provide a great amount of useful data. Of course, the technique itself can introduce numerous errors if great caution is not utilized and a full understanding of the methodology and limitations are not known and evaluated for a given type of samples.
As the general problems associated with the technique have become better understood in recent years, stable-isotopic analyses have begun to make a major impact on investigations of trophic interrelationships in marine and terrestrial ecosystems (e.g., Rau, et al., 1989; Hobson, et al., 1994; Michener and Schell, 1994).
Matt Parry will make the study of the feeding and trophic relationships of the red squid the basis for his dissertation. This study will also involve some analyses of the predators of the red squid, especially the swordfish. We will be searching for additional funding for this study but request that PFRP provide funds to analyze samples in hand and those collected during the 1999 cruise.
Hobson, K. A., J. F. Piatt, and J. Pitoccelli, 1994. Using stable isotopes to determine seabird trophic relationships. Journal Animal Ecology, 63: 786-798.
Michener, R. H. and D. M. Schell, 1994. Stable isotope ratios as tracers in marine aquatic food webs. p. 138-157. In: Lajtha and Michener (eds). Stable Isotopes in Ecology and Environmental Science. Methods in Ecology. Blackwell, Boston.
Rau, G. H., T. Takahashi and D. J. D. Marais, 1989. Latitudinal variations in plankton d13C: implications for CO2 and productivity in past oceans. Nature, 341: 516-S18.
This page updated September 17, 2012