The Lobster Newsletter July 1995
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VOLUME EIGHT JULY 1995 NUMBER ONE 1 RESEARCH NEWS %e‘St det 66 '\TSHERIES AND A Trans-Atlantic Perspective on QUACULTURE Homa rus Recruitment UPDATE FROM: RICHARD A. WAHLE LOBSTER FISHERIES OF INDIA For the better part of a decade scientists in New England and the Cana- dian Maritimes have made important strides in understanding the pro- cesses that in fluencing the benthic recruitment of the American lobster. FROM: E.V. RADHAKR15HNAN Published reports have identified cobble and boulder as an important nursery habitat for lobsters (Hudon 1987, Wahle & Steneck 1991, Incze & Spiny lobsters form one of the Wahle 1991), and in many ways this habitat remains one of the last fron- most valuable crustacean re- tiers of descriptive benthic ecology. That is because cobble defies tradi- sources of India. The richness of tional sampling techniques. For example, cores and grabs used in sand the lobster fauna is brought about and mud tend to break on cobble, and photo-quadrats just do not tell the by the range of habitats available - whole story. For cobble, the suction sampling method has opened a win- rock and mud through to coral dow not only on early benthic phase lobsters, but on the associated fauna reef. Annual landings increased as well. This tool has allowed us to begin leaming how potentially com- from 350 t in 1965 to 3,000 t in peting species may influence lobster recruitment. Here I make a trans- 1975, but declined sharply to 680 t Atlantic comparison of cobble habitat fauna that reveals dramatically in 1980. The fishery recovered to higher species diversity, but lower numbers of Homarus in Europe than 4,100 t in 1985, but has generally in New England. This suggests a multispecies approach to recruitment declined since then (Fig. 1). Slipper issues is warranted. lobsters also are taken commer- cially. In the autumn of 1994, I worked with John Mercer, of the Shellfish Re- search Laboratory of University College, Galway, Ireland, who coordi- Distribution nated my dive surveys of sites on the southwest coast where a lobster Spiny lobsters are widespread CONTINUED ON NEXT PAGE along the 6,100 km coast of India (which includes the Arabian Sea, the Bay of Bengal, and the RECENT EVENTS Lakshadweep and Andaman and Nicobar Islands). The major fisher- Taxonomic Changes ies are in the northwest (Veravel and Bombay), the southwest (Colachel) and the southeast Two recent bring tidings of a new genus Nephropid publications of (Tuticorin, Mandapam, and Ma- lobster and a new species of the Palinurid genus Palinuslus. dras) (Fig. 2). Among the nine spiny lobsters present, Panulirus Kornfield, Williams and Steneck (1995 Fish. Bull. 93: 97-102) report that polyphagus, P. homa rus, P. orna tus, the Cape lobster of South Africa, Homarus capensis (Herbst, 1792) should and the deep sea lobster, Puerulus be transferred to the monotypic new genus Homarinus. The species is sewelli, are the most significant known from only a few specimens. The known individuals are small commercial species. P. versicolor CONTINUED ON PAGE 9 CONTINUED ON PAGE 12 In New England the picture is fairly both groups. Four other decapod RESEARCH NEWS simple; diversity is relatively low families dominated: xanthid crabs, (Fig. 1). In the Gulf of Maine, galatheids, porcellanids, alpheids. CONTINUED FROM PREVIOUS PAGE Hornarus americanus and Cancer At least two to three species were stock enhancement program was irroratus , the rock crab, are by far found in each family. We were ending its second year of hatch- the two most abundant subtidal indeed disappointed not to find ery-releases (Mercer and Brown, species in cobble. (Carcinus maenas, newly settled H. gammarus even at 1994). I also traveled to the Chan- the green crab, is more abundant "ground-zero" of the Irish release nel Islands, UK, which, dispite intertidally). Cancer borealis, the sites. Despite differences in faunal their small size, have some of the Jonah crab, common as adults in composition, the collective densi- largest lobster landings in Europe. traps, is extremely rare as juveniles. ties were similar on both sides of In the northern Gulf of Maine these the Atlantic, ranging between 20- Remarkably, there are still no decapods were far less abundant 80 individuals per square meter. reports of newly settled European than to the south and west, an his- lobsters in the wild, providing an toric pattern for which the mecha- Small individuals dominated the added challenge for our efforts. By nism is still unresolved. In southern populations (Fig. 2) with size November's end we had sampled New England though, xanthid modes between 5 and 15 mm CL eight sites in three study areas. crabs add to the mix of decapods, or CW which, for a least the por- Here, I compare the diversity, and tend to be most abundant celain crabs, xanthid crabs, and abundance, and diversity of taxa where Cancer is not. snapping shrimp approximates to that noted with equivalent sam- the adult size. Only those species pling effort in New England In Ireland and the Channel Islands, that get much bigger (i.e., greater cobble beds. I restrict this report to in contrast, species diversity was than 30-40 mm), like lobsters and non-hermit crab, shelter-dwelling much higher (Fig. 1), but Homarus Cancer spp., do not maintain life- decapods inhabiting cobbles dur- and Cancer were least abundant in long association with cobble. ing part or all of their lives. Europe despite major fisheries for NEW ENGLAND, USA IRELAND & UK HOMARUS TLôbster 11L.11 ^Z6FCFIL=. NEWSLETTER CANCER Editors: L John Booth MAF Fisheries, Greta Point xANTHIDs P.O. Box 297, Wellington NEW ZEALAND N FAX: (4) 386 0574 E jdb@f rc.maffish.govt.nz Z cALArHE1DS J. Stanley Cobb Department of Zoology University of Rhode Island Kingston R! 02881 USA ALPHEIDS FAX: (401) 792 4256 [email protected] John Pringle Fisheries and Oceans PO Box 550 Halifax B3J 2S7 CANADA FAX: (902) 426 3479 j_prin [email protected] The Lobster Newsletter is cospon- sored by Fisheries & Oceans, Canada and the Rhode Island Sea Grant Program. It is published twice yearly. GIElEN6E1 6 SNE CHANNEL GULF OF MAINE IRELAND ISLANDS, UK Figure 1. Average population densities (+ ISE) of decapod fauna in cobble habitats of New England Please send change of address to John Pringle. and Ireland/Channe! Islands. Each bar represents a study site where twelve 0.5 ml quadrats were suction sampled. SNE = southern New England. -1 The Lobster Newsletter - Volume 8, Number 1: July 1995 Page 2 7 i Why didn't we detect young lob- A second hypothesis is that postlar- but we know very little about the sters? If commercial landings are a val H. gamma rus is not as ecologi- carrying capacity of these habitats reasonable index of abundance, cally similar to H. americanus as as forH. gammarus. For the American it's possible our sampling effort assumed; perhaps it prefers a nurs- lobster though, we have deter- was inadequate to detect ery habitat other than cobble? That mined carrying capacity through H.gammarus. Recent landings of explanation seems unlikely too, saturation seeding experiments of Homarus throughout Europe have however, given the similarity to H. standardized cobble plots where only been about 1/40th of North americanus in shelter-seeking behav- quantity of cobble was manipu- American landings, about equiva- ior and habitat preference (Berrill lated (Wahle & Incze in review). lent to the landings of the state of 1974). All the early benthic phase H. From those experiments carrying Rhode Island. (Ireland and the UK gammarus in a seawater pond at the capacity was estimated to be at the comprise about 3/4 of Europe's hatchery were under rocks, shells, highest benthic recruitment den- landings). Densities of lobsters of and plastic placed on the bottom for sity seen in nature, around 5 - 6/ all sizes in central Maine (USA) cover. Moreover, with the sampling mz. This low putative carrying cobble beds average about 3 - 5/ effort that has gone into other habi- capacity suggests there are space mz; and one-fortieth of that would tats over the years, such as sedi- requirements beyond shelter we give a density of 0.07 - 0.12 /m2. ment coring, one is hard pressed to do not yet understand for the At that density, according to Pois- think what other habitat they might American lobster. son analysis, we would expect our occupy. sampling effort of 108 half-square- Nonetheless, all these taxa seem to meter quadrats to produce 102 New En;;1aIl(i Ireland &-UK have similar habitat requirements, quadrats with no lobsters and 6 but we have little knowledge of with one lobster. Thus, by this CANCER the nature of the interaction. We coarse analysis with no correction clearly need to devise models and for fishing effort or coast length, experiments to test hypotheses, we might have expected very few J1 I because the benefit will be a lobsters. Our less systematic vi- greater insight into the recruit- sual searches, totaling five addi- ment process as wcll as the effi- tional dive-hours, did produce cacy of stock enhancement. In any two lobsters: a large berried fe- case, there seems to be a need to male at 110 mm CL, and a juvenile go beyond the single species ap- at 40 mm. proach to fully understand the factors that influence recruitment Why would the European lobster of a target fishery like Homarus. be rare in cobble if it is ecologi- cally similar to the American lob- LITERATURE CITED ster? Several untested hypotheses exist. First, fishing has undoubt- Berrill, M. 1974. J. Mar. Biol. Ass. UK 54: 797-801.