Marine Invertebrate Conservation: Evaluation of Fisheries Over-exploitation Concerns

The nature of overfishing of marine invertebrates is complex,ranging from the perception of overfishing because of competitionby user groups for a common property resource to extensive overfishingto near extinction because of poaching by either licensed orunlicensed fishers. As a group, marine invertebrates seem particularlyresistant to overfishing, primarily because their relative immobilityand scattered concentrations means refuge populations oftenexist. However, this distribution pattern also means a fisheryis scattered over an often large geographical area with relativelysmall, frequent landings at any location. A minimum legal sizeregulation, enforceable anywhere before consumption, is theprimary regulation applied by managers for many species to ensureagainst overfishing. Overfishing concerns arise primarily forthose species where price is sufficiently high to encourageillegal fishing or where harvest by fishers is not easily monitoredor controlled because of the nature of the fishing activityor because only part of the animal (e.g., the flesh) is harvested.Instances of overfishing by cause are discussed, and examplesare presented to demonstrate how managers are dealing with orhave dealt with different situations.     

Life history and production of the predatory caddisfly Rhyacophila vao Milne in a spring-fed stream

1. The predatory caddisfly Rhyacophila vao Milne (Rhyacophilidae) displayed a 2-year, semivoltine life cycle in a small, spring-fed stream in southern Alberta, Canada. Three overlapping cohorts were identified throughout the 2-year sampling program, with five larval instars recognized. Larvae overwintered in instars I —ELI, developed to instar IV by summer and instar V by autumn. The second winter was spent in instar V, Pupation occurred from late May to August and did not commence until stream temperature exceeded 3°C. Adults were collected from mid-June to early September. 2. Larvae displayed a diphasic growth pattern: Phase I, a positive, non-linear growth rate for instars I-IV; Phase II, a constant growth rate during instar V. Phase I coincided with increasing stream temperatures in late winter and spring, where mean instantaneous growth rates (maximum of 2.78% dry wt day^?1) were significantly correlated with stream temperatures. Although the duration of Phase II spanned a temperature range similar to that in Phase I, the instantaneous growth rate remained temperature-independent at 0.87% dry wt day^?1. 3. Larvae exhibited a type III survivorship curve (i.e. an exponential decrease on an arithmetic scale), with the finite rate of mortality averaging 0.80% larvae day^?1. 4. Cohort 1 (later part of 1983 year class) displayed lower total production compared with the equivalent growth phase in the 1984 year class (Cohort 2). In contrast, production of the non-linear and linear growth phases of Cohort 2 was similar. Periods of similar growth characteristics for Cohorts 1 and 2 had comparable P/B ratios for both the unadjusted and time-adjusted annual estimates, although higher ratios were observed for the non-linear growth phase of Cohort 2. Total cohort production (linear + non-linear growth phases) could only be calculated for Cohort 2, and was 870.2 ± 1011.4 mg dry wt m^?2. The corresponding cohort P/B ratio was 5.01 and the adjusted annual P/B, 3.01. 5. Annual larval production (±SE) for the first and second years of the study was similar (Year 1, 480.0 ± 387.5mg dry wt m^?2; Year 2, 526.9 ± 967.5mg dry wt m^?2) as were unadjusted and annual P/B ratios.     

Ultrastructure of the Tubificid Acrosome (Annelida, Oligochaeta)

The later morphogenesis of the acrosome of Limnodriloides winckelmanni and Rhyacodrilus arthingtonae is compared with that in Enchytraeus and in earthworms. After superposition of the acrosome on the tip of the nucleus the manchette continues apically beyond the nucleus to ensheath the acrosomal tube. At the posterior limit of, and probably contained in, the spacious/ terminal primary acrosomal vesicle is an electron-dense ring. A domed protrusion into the floor of the primary vesicle is tentatively regarded as the secondary acrosome vesicle. The axial rod when first observed is attached to the vesicle complex. Later, the rod detaches and extends deeply into the acrosome tube. A membrane ensheathes the tubificid axial rod but its exact homology with the complex layers surrounding the lumbricid or megascolecid axial rod is not clear. The domed apical region of the tubificid acrosome is probably a persistence of the primary acrosome vesicle and it is deduced that the acrosome vesicle surrounding the axial rod in lumbricids and megascolecids is a product, by invagination, of the secondary acrosome vesicle only.     

Assessment of ecological status in U.K. rivers using diatoms

1. The European Union's Water Framework Directive requires all water bodies to achieve ‘good ecological status’ by 2015 and this paper describes a rationale for defining ‘good ecological status’ based on diatoms, a significant component of the biological quality element ‘macrophyte and phytobenthos’. 2. A database of benthic diatom samples collected over the past 20 years was assembled. New sampling, specifically for this project, was undertaken during 2004 to supplement these data. In total 1051 samples were included in the database with matching environmental data. 3. ‘Reference sites’, relatively unimpacted by human activity, were selected from this database by a series of screening steps and these sites were used to develop a site‐specific reference typology. 4. Environmental variables not related to the pressure gradient were used to predict the ‘expected’ Trophic Diatom Index (TDI) values at each site. Site‐specific TDI predictions were used to generate ecological quality ratios (EQRs) ranging from ≥1, where the diatom assemblage showed no impact, to (theoretically) 0, when the diatom assemblage was indicative of major anthropogenic activities. 5. The boundary between ‘high’ and ‘good’ status was defined as the 25th percentile of EQRs of all reference sites. The boundary between ‘good’ and ‘moderate’ status was set at the point at which nutrient‐sensitive and nutrient‐tolerant taxa were present in equal relative abundance. An ecological rationale for this threshold is outlined in the paper.     

Low reproductive success of the endangered Takahe Porphyrio mantelli on offshore island refuges in New Zealand

Many of New Zealand's endangered birds have been transferred from the “mainland” of the North and South Islands to smaller coastal islands free from introduced predators and competitors. The transfer of Takahe Porphyrio mantelli (Plate 1) to offshore islands is unique because these highly endangered, flightless rails are being moved from alpine-tussock habitat of Fiordland, the last remaining natural population, to substantially different lowland habitat on island refuges. Despite the fact that 30% of the approximately 160 Takahe left in the wild now live on coastal islands, a detailed analysis on the success of the island populations has never been undertaken. Using data available from New Zealand's Department of Conservation, we found that while adult survivorship of Takahe on islands is high, reproductive success is significantly lower than in Fiordland. Most factors examined, including inbreeding and nutrient deficiency, had no significant effect on reproductive success of Takahe breeding on islands. Island pairs produced fewer eggs and juveniles in the first year of their pair bond relative to all other years. Hence the large number of transfers of birds between islands during the initial stages of the relocation program may have resulted in a higher frequency of pair formation and thus may have contributed to the islands' lower reproductive success. Why first clutches did so poorly (four juveniles from 43 clutches) compared with second (11 from 36) and third (six from 13) clutches is not known but was one of the main contributing factors for island pairs making greater nesting effort but significantly lower returns than birds breeding in Fiordland. In addition, some individual birds have been very successful in producing young relative to other birds, suggesting that important differences in quality of some breeders may also exist. We expect island productivity will improve over time as the number of interisland transfers of Takahe decreases and as the proportion of breeding birds raised in the island environment increases.     

AN ULTRASTRUCTURAL STUDY OF SPERMATOZOA OF HELIX ASPERSA AND HELIX POMATIA (GASTROPODA, PULMONATA)

Spermatozoa of the pulmonates Helix aspersa Müller andH. pomatia Linnaeus are examined in detail using transmissionelectron microscopy (TEM). Important features such as the acrosome,perinuclear sheath, nucleus and terminal region of the midpieceare described for the first time. Also presented are the firstultrastructural observations on spermatozoa from spermatophoresin any pulmonate gastropod (H. aspersa). No morphological differencescould be found between sperm taken from spermatophores and thosewithin the hermaphrodite duct in H. aspersa. Spermatozoa ofH. aspersa and H. pomatia snow all the characteristics of euthyneuranspermatozoa, namely: a helically-keeled nucleus; distinctivearrangement of acrosomal components (apical vesicle, acrosomalpedestal), and extremely elongate midpiece (axoneme and glycogenhelix enclosed by matrix and paracrystalline layers). The spermnucleus of both species is short, and the midpiece also formsthe terminal portion of the spermatozoon (glycogen piece absent).The extraordinary positioning of the acrosome in H. aspersa—reflectedbackwards from the nuclear apex—is not observed in H.pomatia, though a perinuclear sheath (possibly another acrosomalcomponent) is present in sperm of both species. Helix spermatozoaare compared with other euthyneuran sperm and briefly discussedfrom the systematic viewpoint. Present address: Department of Zoology, St. Lucia, 4067, Brisbane,OLD, Australia (Received 23 May 1988; accepted 17 August 1988)     

The identification of an aphid juvenile hormone, and its titre in relation to photoperiod

ABSTRACT. Whole body extractions from larval and adult apterous forms of Megoura viciae , and from adult Aphis fabae , were analysed for the known insect juvenile hormones (JHs) by a gas chromatography-mass spectrometric method. Low levels of JH III were detected in both aphid species, the first identification of a juvenile hormone from an homopteran insect. Although the mean titre in adult M. viciae is higher in long-day than in short-day reared insects (0.12±0.03 v. 0.04±0.01 ng/g), titres were variable and measurements overlapped. The results are discussed in the context of the hormonal control of aphid polymorphism and the question of identity of homopteran and hemipteran JH.