RESEARCH INTO the LIFE HISTORY of Lollgo OPALESCENS: WHERE to from HERE? GEORGE D

JACKSON: RESEARCH NEEDS FOR LOLlGO OPALESCENS CalCOFl Rep., Vol. 39, 1998

RESEARCH INTO THE LIFE HISTORY OF LOLlGO OPALESCENS: WHERE TO FROM HERE? GEORGE D. JACKSON' James Cook University Departiiient of Manne Biology Townsville, Qurensland 481 1 Australia

ABSTRACT history of these loliginid populations worldwide to pro- Statolith ageing techniques have greatly aided our un- vide the necessary building blocks for management and derstanding of loliginid squid biology. We now know policy decisions. Without such data, management is based that life spans of loliginid squids are relatively short: most only on guesses and approximations. Current knowl- temperate species live for about a year or slightly more. edge about the age and growth of loliginid squids has Many tropical species appear to complete their life revealed that previous life span estimates have led to an spans in fewer than 200 days. Early growth estimates inaccurate understanding of the biology of these orga- for Loligo opalescens based on length-frequency analysis nisms. One example of this has been the application of have suggested a life span of around two years. However, length-frequency analysis in an attempt to determine preliminary data from statolith ageing and culture of squid growth (see Jackson and Choat 1992; Jackson et L. opalescens have shown that reproductive maturity can al. 1997). The results of such analysis have led to the be reached in less than a year. Further research is needed measurement of life spans in years instead of days. Such to determine the life span of this species, but it is pos- errors can have profound implications for interpreting sible that it may not exceed one year. Research is espe- population dynamics and for management decisions. cially needed to vahdate periodicity in statolith increments The collection of accurate data on age, growth, and and to study latitudinal and seasonal variation in growth life history is fundamental for implementing long-term and maturity rates. This will provide the necessary data management strategies. This paper reports on past re- for future management and policy decisions. Other areas search into the age, growth, and life lustory of L. opalesceris; of research-the use of predators as sampling tools; in- identifies where we are now; and suggests areas where vestigation of the condition of and degradation of tissue research should be focused. The significance of apply- in association with maturity; tracking studies using trans- ing ageing techniques to L. opalescens can be appreciated mitters, rad0 acoustic positioning, and telemetry (RAPT) by drawing on the results of studies from other lolig- as well as traditional tagging; and light trapping-may inid populations (summarized in table 1) that have used yield important biological data about L. opalescens. similar ageing techniques to determine important biological features. INTRODUCTION Loligo opalescens is not only a valuable fishery resource Loliginid squid stocks occur in most continental shelf but also an important ecological species in the California areas of the world's oceans except for the extreme polar Current. Its predators include at least 19 species of fish, regions. Some species have a wide latitudinal distribu- 13 species of birds, and 8 species of marine inaimnals tion, such as Loligo opalescens off the west coast of North (Morejohn et al. 1978). Some vertebrates reviewed in America or Loligoforbesi in EuropeadAfrican waters. In Morejohn et al. (1978) that appear to be niajor predators contrast, Sepioteuthis australis, which is restricted to south- of L. opalescens include the fish curlfin turbot (Pleuronichthys ern Australia and northern New Zealand waters, is an decurrens), several specimens of which have been shown example of a loliginid with a much narrower distribu- to consume more than 600 indwidual squid; the seabirds tion. In some continental shelf regions (e.g., northern rhinoceros auklet (Cerorhinca monocerata) and sooty shear- Australia; Yeatman and Benzie 1993, 1994, or the Gulf water (Puflnusgriserrs); and the marine mammals harbor of Thailand; Chotiyaputta 1993) there is a diversity of porpoise (Phocoena phocoena) and the California sea lion loliginid species, whereas in other regions there is only (Zalophus cal$rniarzus). Management of L. opalescens stocks one loliginid species, such as L. galzi on the Patagonian therefore extends beyond fisheries interests alone; it must Shelf and L. opalescens off California. also take into account the role of this species in the ecol- Many of these populations are coming under increasing ogy of California coastal waters. pressure from national and international fisheries. There is a need to obtain information on the biology and life LIFE HISTORY OF LOLlGO OPALESCENS Loligo opalescens is a nearshore loliginid squid that in- 'Pre~entaddress: University of Tasmania, Institute of Antarctic and Southern habits continental shelf waters off the west coast of North Ocean Studies, GPO Box 252-77, Hobart, Tasmania 7001, Australia. georgejacksonmutas.edu.au America. A key feature of its life cycle is the spawning

101 JACKSON: RESEARCH NEEDS FOR LOLlGO OPALESCENS CalCOFl Rep., Vol. 39, 1998

Figure 1. The ground and polished statolith of a female Loligo opalescens (128 mm mantle length, age 31 1 d; see Jackson 1994b) captured off central California in 1990: A, whole statolith (scale bar = 500 pm); B. close-up of lateral region showing detail of increment structure (scale bar = 100 vm); C, close-up of individual increments in the lateral region (scale bar = 50 pm). aggregation which takes place in relatively shallow waters periodicity in production of statolith increments has been off California. Before reproducing, squid appear to be validated in a number of species Qackson 1994a;Jackson more dispersed, with some individuals in deeper water. et al. 1997). Statolith analysis reveals information on hatch For spawning, they form huge aggregations and produce date, individual age, and average growth rates (fig. 1). benthic egg masses that can be up to 12 m in diameter Analysis of the width of daily rings may also provide in- and over a meter in depth (Hixon 1983). formation on daily growth. There is now the potential This species appears to be a true terminal spawner, for using the squid gladus to analyze specific daily growth with death following soon after spawning. Analysis of the rate (Arkhipkin and Bizikov 1991; Bizikov 1991;Jackson reproductive system of males (Grieb and Beeman 1978) et al. 1993; Bizikov 1995; Perez et al. 1996). and females (Knipe and Beeman 1978) revealed that the Spratt (1978) highlighted the significance of incre- maturation process is terminal; there is no sign of re- ments within the statoliths of L. opalescens when statolith newal of the gametogenic process in males and no stage analysis was in its infancy. Although Spratt identified I preoocytes in females. There is also a dramatic emaci- what he thought were daily increments within the dor- ation of the mantle tissue in association with niatura- sal dome of the statolith, he also suggested that more tion; its thickness decreases approximately 24% in males prominent increments were produced monthly. Enu- and 42% in females (Fields 1965, cited in Hixon 1983). meration of these daily as well as “monthly” increments also indicated a life span of almost two years. AGE AND GROWTH Culture of L. opalescens provided another avenue to Growth estimates for L. opalescens have come from understanding growth parameters and life span. Work by length-frequency analysis, culture data, and limited use Yang et al. (1983, 1986) resulted in a radically different of age information. Fields (1965, cited in Hixon 1983) form of growth. Cultured individuals could be modeled used length-frequency analysis in an early attempt to un- by an exponential equation, and maturity was reached in derstand growth. These early results suggested a growth captivity in less than 200 d, with spawning taking place rate of 4 mm/month and a life span of about two years. between 196 and 239 d. Culture work yielded consid- Knowledge of squid biology has been greatly enhanced erably different life-span estimates for L. opulescens than with the discovery of daily statolith increments. There previous fieldwork, which suggested a life span of about is a growing body of information on growth and life two years (fig. 2). spans of squids based on data obtained from statoliths A second preliminary analysis of statolith growth in- (Rodhouse and Hatfield 1990;Jackson 1994a). The daily crements was undertaken by Jackson (1994b), who aged

102 JACKSON: RESEARCH NEEDS FOR LOLlGO OPALESCENS CalCOFl Rep., Vol. 39, 1998

1751 - - - - - Yang ef a/. (1986) II I50 - + + + 125 - + 00 0

100- h E

dE 2 75-

50 -

25 -

36 9 12 15 18 21 24 Age (mths) Figure 2. Summary of growth models developed for Loligo opalescens X Cultured (modified from Hixon 1983). -k Males 0 Females

12 individuals of L. opalescens captured off Monterey, I I I I I I in central California. This analysis interpreted all in- 0 50 100 150 200 250 300 350 crements as daily, in contrast to earlier work by Spratt Age (days) (1978). The good agreement in the results of Jackson Figure 3. Age estimates for field-captured individuals of Loligo opalescens compared to data generated for this species raised in captivity (from Jackson (1994b) and Yang et al. (1986) suggests that L. opalescens 1994b). may complete its life in less than a year off central California (fig. 3). (e.g., Forsythe 1993). Age analysis of field-caught indi- Such studies underscore the significance and validity viduals (Jackson and Choat 1992) revealed seasonal vari- of ageing studies for understanding squid growth, and ation in growth in the tropical loliginid Photololigo sp. further reveal the inadequacies of applying length- (referred to as Loligo chinensis, but now known to frequency analysis to squid. be a new species; see Yeatman and Benzie 1993, 1994), which completed its life span in 115 d in summer but INFORMATION FROM lived longer than 170 d in winter. These differences in OTHER LOLlGlNlD POPULATIONS growth rates also affected seasonal maturation rates in An examination of age and growth parameters from the species (Jackson 1993). other loliginid populations can provide general features Ageing work on Loligo gahi (Hatfield 1991) and Ldigo of age and growth of loliginids. Statolith ageing tech- pealei (Brodziak and Macy 1996) also showed that indi- niques have now been applied to a number of loliginid viduals which hatched in different months had differ- populations around the world (table 1). The results re- ent growth rates. Recent work on Loliguncula brevis veal that loliginid life spans are generally short; only sev- (Jackson et al. 1997) revealed that small, shallow-water eral species live longer than a year, and all species coniplete lolignids can exhlbit marked seasonal dfferences in growth their life cycles in fewer than 18 months. Loligo vulgaris as a result of pronounced seasonal temperature fluctua- reynaudii appears to have one of the longest life spans; tions. The age of this species can range from 81 to 172 some large males may live longer than 15 months (Lipinslu d, depending on the prevailing temperatures during 1991; Augustyn et al. 1994). Generally, temperate species growth (especially during the early growth period). complete their life cycle in about a year; tropical species Seasonal growth variation is so important that ageing can complete their life cycle in <200 d; and very small individuals without a knowledge of their past life his- tropical species such as Loliolus noctiluca can reach maturity tory would make it virtually impossible to understand in 3 months or less and complete their life cycle in 4 the form of growth. For example, figure 4a shows all the months (Jackson and Choat 1992). age data for Loll&uncula brevis from Jackson et al. (1997). Loliginid squids show a marked response to environ- Presenting this data without a knowledge of the season mental temperature changes because of their short lives of capture can mask the form of growth. The scatter- JACKSON: RESEARCH NEEDS FOR LOLlGO OPALESCENS CalCOFl Rep., Vol. 39, 1998

TABLE 1 Size and Age Data from Different Loliginid Populations around the World, on the Basis of Statolith Age Analysis

Region Species Age (days) Mantle length (mm)a Environment Reference North America 280 142 Temperate Jackson 1994h 296 303-440 Temperate Macy 1995 172 sunliner 72 Wariii temperate Jackson et al. 1997 95 winter 71 81 autumn 82 South America -139 210-350 Temperate Hatfield 1991 Europe 377 male 33 1 Temperate Collins et al. 1995 359 female 263 -245 -274 (not full merange) Warm temperate Natsukari & Komine 1992 North Africa 396 male 498 Tropical Arkhipkin 1995 335 female 290 208 male 205 Tropical Arkhipkin & Nekludova 1993 187 female 1 s5 231 male 135 Tropical Arkhipkin & Nekludova 1993 172 femalc 72 South Africa -.540 360 Temperate Lipinski 1991 Japan 3.50 -404 Wami temperate Natsukari et a1 1988 385.5 male 320 Warm temperate Kinoshita 1989 336.5 fm1ale 210 Thailand 172 male 27 1 Tropical Chotiyapiitta 1997 151 female 235 98 iiiale 119 Tropical Chotiyaputta 1997 9s felndle 110 Australia 188 184 Tropical Jackson 199Oa 173 wiuter 167 Tropical Jackson & Choat 1992 1 15 sunnier 167 -102 -92 Tropical Moltschaniw$kyj 1995 P/lorlllo/~,lsp. 1 157 115 Tropical Jackson &- Yeatman 1996 Lolioh4s rioctibca 112 90 Tropical Jackson &- Choat 1992

~ Age and mantle length values were generally provided in the reference or estiinated from size-at-age plots iiicluded in it. ,'The data refer to sizes of oldest individuals, which do not necessarily indicate the maxiinun~obtainable size for each species. 'This species was referred to as Lol~& cliiricvrsis in lackson and Choat 1992. It is now known to he ne\\., undescribed species of Pliot~il~iliji~i(see Yeatman and Benzie-1993, 1994)

plot in figure 4a suggests that L. brevis niight have asymp- larger size (Moltschaniwskyj 1994). Squid also show both totic growth, with a slowing after about 100 d, and a life niechanisnis of muscle fiber growth, but with the fun- span of about 170 d. However, when the data are plot- damental difference that hyperplasia does not cease; rather, ted with the appropriate seasonal segregation (fig. 4b) recruitment of new muscle fibers is a continuous process it becomes apparent that growth is nonasymptotic; squids throughout life. This phenomenon has also recently been that hatched during warmer seasons had faster growth documented for L. opalescens (Preuss et al. 1997). rates and shorter lives. Results of ageing work on squid suggest that growth FUTURE RESEARCH is continuous, nonasymptotic, and exponential or linear in form. In many species, growth of the gonad appears Growth and Reproduction to coincide with growth of the soma. We currently do The growth of L. opalescens is still poorly understood. not fully understand all the physiological processes gov- Because of its wide latitudinal distribution, this species erning how squid grow. They do, however, appear to encounters considerable temperature differences. It is grow in a fundamentally different way than fish (e.g., therefore likely to exhibit marked plasticity in growth as O'Dor and Webber 1986; Alford and Jackson 1993). a result of varying water temperatures. Growth may also Moltschaniwskyj (1994) has provided a physical mech- differ depending on the season of hatching or other phys- anisni for the observed differences in the form of growth ical phenomena such as El Niiio events. between squid and fish. Fish appear to grow initially by There appears to be a continuum in squid reproduc- recruitment of new muscle fibers (hyperplasia) and with tive strategies, from species that are multiple (or batch) an increase in muscle fiber diameter (hypertrophy). Their spawners (e.g., Stenoteuthis oualaniensis, Harman et al. final size may be influenced by the number of muscle 1989; Lol{qoforbesi, Boyle et al. 1995) to true terminal fibers present once hyperplasia ceases, and individuals spawners chat die in association with or soon after spawn- with more muscle fibers have the potential to reach a ing (e.g., L. opalescens, Grieb and Beeman 1978; Knipe JACKSON: RESEARCH NEEDS FOR LOllGO OPAESCENS CalCOFl Rep., Vol. 39, 1998

90 - A 2. Validation experiments should be undertaken to 80 - 70 - 0 document the periodicity of statolith increments. 60 - This would involve staining live squid with either 50 - tetracycline or calcein (e.g.,Jackson 1989, 1990a, b) 40 - 30 - and maintaining individuals in captivity to verify the 20 - 0 one-ring:one-day hypothesis. Alternatively, other 10’ I - I , techniques such as analysis of marginal increments 40 60 80 100 120 140 160 180 200 Age (days) for individuals captured over a 24 hr period may be possible (Jackson 1994a). 3. Studies into squid condition in association with maturation should be undertaken to describe the dynamics of mantle muscle in association with terminal spawning. If a process of tissue degradation occurs in L. opalescens similar to that in M. ingens, then females nearing the end of their lives may have l0J I - I I 40 60 80 100 120 140 160 180 200 very little muscle tissue left. Age (days) 4. Examine the possibility of using predators as sam- Figure 4. Size-at-age data for Lolliguncula brevis from the Gulf of Mexico pling devices. Squid are notoriously chfficult to sam- (Jackson et al. 1997). A, The scatterplot resulting from pooling all individuals, with the data suggesting a possible asymptotic growth curve; B, the same ple, especially the younger stages. But some species scatterplot showing the month of collection and the associated exponential such as the curlfin turbot may prove to be excel- growth curves. Note that neither the x nor the yaxis starts at zero. lent sampling devices for juvenile squid. Croxall and Prince (1996) have highlighted the usefulness and Beeman 1978; Moroteuthis ingens, Jackson and of seabirds for sampling squids. Some species such Mladenov 1994). The physical processes of terminal as the rhinoceros auklet rriay also be an effective spawning in L. opalescens need to be described in more sampling tool. Species that prey on younger stages detail. The deepwater squid M. ingens was shown to may offer a valuable means for sampling the rela- undergo a dramatic tissue breakdown process in associ- tive abundance of juvenile squid in order to pre- ation with maturation and spawning that results in the dict future recruitment into the adult population. loss of virtually all mantle musculature, leaving only a Alternatively, periodic collections of scats or vom- collagen matrix. The loss of mantle thickness in L. its of the California sea lion may offer an effective opalescens (Fields 1965, cited in Hixon 1983) may be due way to monitor the population structure of squid to a similar process. in a specific region. Such analysis is especially ef- Potential Research Protocols fective because specific squid species can be identified by undigested beaks (e.g., Klages 1996), and Although there are some historical data on the biol- beak size can be related to squid size (Clarke 1986). ogy of L. opalescens, there is an urgent need to establish Examining such remains should make it possible biological parameters for this species. Such life-history to reconstruct size frequencies of squid. data can then be used to develop necessary management 5. Radio acoustic positioning and telemetry (RAPT) models. The following studies would greatly facilitate offers one means of obtaining information on our understanding of L. opalescens biology. movements of individuals within a spawning re- 1. Obtain information on age, growth, maturation gion over small scales of hundreds of meters to sev- rates, and life span from analysis of statolith incre- eral kilometers (e.g., Sauer et al. 1997). Individual ments. Statoliths are the tools of choice for deter- squid can be tracked over longer distances with mining the basic demographic parameters needed telemetry (e.g., Nakainura 1991) to obtain infor- for population management. Since L. opalescens cov- mation on longer migrations or movements into ers such a large latitudinal range (Alaska to Mexico, deeper water offshore. Traditional tagging nieth- Hixon 1983), samples should be taken from a va- ods (Nagasawa et al. 1993; Takami and Suzu- riety of sites covering as large a latitudinal range as uchi 1993) may also be useful for obtaining infor- possible. This will document the geographic vari- mation on long-distance migrations along the ability in growth rates. Sampling effort should also California coast. be conducted year-round, and should span several 6. Light trapping (MoltschaniwskyJ and Doherty 1995) years from one or more key sites to document dif- may be a technique for monitoring the abundance ferences in growth rates, maturation rates, and life and distribution of juvenile squid within the water spans of different seasonal cohorts. column.

105 JACKSON: RESEARCH NEEDS FOR LOLlGO OPALESCENS CalCOFl Rep., Vol. 39, 1998

CONCLUSION Croxall,J. P., and P. A. Prince. 1996. Cepalopods as prey. I. Seabirds. Philos. Trans. R. Soc. Lond. U 351:1023-1043. California management agencies are in a unique po- Fields, W. G. 1965. The structure, developiiient, food relations, reproduc- sition to collect basic biological data on L. opalescens be- tion, and life history of the squid Lol@ opalesrens Uerry. Calif Dep. Fish fore fishing pressure increases. As the fishery progresses, Game, Fish Bull. 131, 108 pp. (cited in Hixon 1983). Forsythr, J. W. 1993. A working hypothesis on how seasonal temperate ongoing monitoring and assessment will provide basic change niay impact the field growth ofyoung cephalopods. In Recent ad- biological information that can serve as a basis for de- vances In cephalopod fisheries bioloby, T. Okutani, R. K. O'Dor, and veloping management strategies. We still do not fully T. Kubodera, eds. Tokyo: Tokai Uiiiversity Press, pp. 133-143. Grieb, T. M., and R. 11. Beeiiian. 1978. A ctudy of sprrniatogenesis in the understand the importance of L. opalescens off the North spawning population of the squid, Loliyo opalescens. Dep. Fish. Game. Fish. American coastline. Continued research with a varietv Dull. 169:ll-21. of techniques will help to answer important biological Harmon, R. F.. R. E. Young, S. B. Reid, K. M. Mangold, T. Suzuki, and R. F. Hixon. 1989. Evidence for multiple spawning in the tropical oceanic questions that are now being ..asked. Such focused re- squid Stcnoteutliis oiraln~iir~isis(Teuthoidea: Ommastrephidae). Mar. Biol. search will also serve ecological" and conservation needs 101:5 1 3-51 9. because the resulting data will help to clarify the role Hatfield, E. M. 1991. Post-recruit growth ofthe Patagonian squid Loligogalii (D'Orbigiiy). Bull. Mar. Sci. 49349-361. that L' opa'escens plays in the California coastalfood web. Hixon, R. F. 1980. Loligo-- op~l~iie~~. ZW Cephalopod.- life cycles, vol. 1, P. R. Boylr, ed. London: Academic Press, pp. 95-1 14. ACKNOWLEDGMENTS Jackson, G. 11. 1989. The use of statolith inicrostructures to analyze life- history events in the small tropical cephalopod Idiosepirrs pypaaus. Fish. I would like to thank the California Seafood Council Bull. 87:265-272. for covering the cost to attend the 1997 CalCOFI con- . 1990a. Age and growth of the tropical near shore loliginid squid ference; Thomas, who assisted with figure preparation; Sapioteurliis Imssoniaria determined from statolith growth ring analysis. Fish. R. Bull. 88:113-118. and C. Jackson for help with manuscript preparation. . 1990b. The ure of tetracycline staining techniques to determine statolith growth ring periodicity in the tropical loliginid squids Loliolns Jloc- tilura and Lolip cliifien5s. Veliger 33:395-399. LITERATURE CITED . 1993. Seasonal vanation in reproductive investment in the tropical Alford, R. A,, and G. D. Jackson. 1993.110 cephalopods and larvae of other loliginid squid Lo/& rliiriensis and the small tropical sepioid Idiosepins pyx- taxa grow asymptottcally? Ani. Nat. 141:717-728. niaeus. Fish. Uull. 91 :260-270. Arkhipkin, A. 1995. Age, growth and maturation of the European squid . 1994a. Application and future potential of statolith iiicrement analy- Lol~&i vu@is (Myopsida, Loliginidae) on the West Saharan Shelf. J. Mar. sis in squids and sepioids. Can. J. Fish. Aquat. Sci. 512612-2625. Biol. Ass. U.K. 75:593-604. . 1994b. Statolith age estimates of the loliginid squid Loligo opalrsrefzs Arkhipkin, A. I., and V. A. Dizikov. 1991. Coinparative analysis of age and (Mollusca: Cephalopoda), corroboration with culture data. Bull. Mar. Sci. growth rates estimation using statoliths and gladius in squids. In Squid age 54:.554-5.57. determindtion using statoliths, P. Jereb, S. Ragoiiese and S. v. Uoletzky, Jackson, G. D., arid J. H. Choat. 1992. Growth in tropical cephalopods: an eds. Proceedings of the international workshop held in the Istituto di analysis based on statolith niicrostriicture. Can. J. Fish. Aquat. Sci. Teciiologia della Pesca e del Pescdto (ITPP-CNR), Mazara del Vallo, Italy, 4921 8-228. 9-14 October 1989. N.T.K.-I.T.P.P. Spec. Publ. no 1, pp. 19-33. Jackson, G. D., and P. V. Mladenov. 1994. Trrniinal spawning in the deep- Arkhipkin, A. I., and N. Nekludova. 1993. Age, growth and maturation of water squid .bIoriiteiitliis iyps (Cephalopoda: Onychoteurhidae). J. Zool. the loliginid squids Allofiuflzisn/n'ca~ia and A. sitbnlatn on the West African Lotld. 234:189-201. Shelf. J. Mar. Biol. Ass. U.K. 73:949-961. Jackson, G. D., and J. Yeatman. 1996. Variation in sizz aiid age at niatunty Augustyn, C. J., M. R. Lipinski, W. H. H. Sauer, M. J. Roberts, and U. A. in P/m/o/igil(Mollusca: Cephalopoda) from the northwest shelf of Australia. Mitchell-Innes, 1994. Chokka squid on the Agulhas Bank: life history and Fish. Bull. 94:59-65. ecolobT. S. Air. J. Sci. 90:143-154. Jackson, G. D., A. I. Arkhipkin, V. A. Dizikov, arid R. T. Hanlon. 1993. Bizikov, V. A. 1991. A new method of squid age detemunation using the gla- Laboratory and field corroboration of age and growth froin statoliths and dius. In Squid age detemiination using statoliths, P. Jereb, S. Ragonese and gladii of the loliginid squid Sepiorentliir lcssoniana. IJJKecent advances in S. v. Boletzky, eds. Proceedings of the international workshop held in the cephalopod fisheries biology, T. Okutani, K. K. O'Dor, and T. Kubodera, Istituto di Tecnologa della Pesca e del I'escato (ITPPCNR), Mazara del eds. Tokyo: Tokai University Press, pp. 189-199. Vdo, My, 0-14 October 1989. N.T.R.A.T.P.P. Spec. Publ. no 1, pp. 3!%5l. Jackson, G. D., J. W. Forsythe, R. F. Hixon, and R. T. Hanlon. 1997. Age, -. -. 1995. Growth of Steriotrnrliis oualanicwsis, using a new method based growth and maturation of Lnllip~i~i~labrevis (Cephalopoda: Loliginidar) in on gladius microstructure. ICES Mar. Sci. Symp. 199:445-458. the northwestern Gulf of Mexico with a comparison of length-frequency Boyle, P. I<., G. J. Piercc, and L. C. Hastie. 1995. Flexible reproductive strate- vs. statolith age analysis. Can. J. Fish. Aquat. Sci. 54:2907-2919. gies in the squid Loli,oo.fiir6esi. Mar. Biol. 121:SOl-508. Kinoshita, A. 1989. Age and growth of lolignid squid, Heterldqo bleekcri. Brodziac, J. K. T., and W. K. Macy 111. 1996. Growth of long-finned squid, Bull. Seikai Reg. Fish. Kes. Lab. 6757-69. LJ/@Ipealei, in the northwest Atlantic. Fish. Bull. 94:212-236. Klages, N. T. W. 1996. Cephalopods as prey. 11. Seals. Phil. Trans. R. Soc. Chotiyaputta, C. 1993. A survey on diversity and distribution of juvenile Lond. B 351:1045-1052. squids in the inner and western Gulf of Thailand. Thai Mar. Fish. Res. Knipe, J. H., and R. D. Beernan. 1978. Histological observations on oogen- Bdl. 4.1 9-36. esis 111 Lolip opalescens. Dep. Fish. Game. Fich. Bull. 16923-33. . 1997. 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