S. J. G. Hall

Fishing and the ground-fish assemblage structure in the north-western North Sea : an analysis of long-term and spatial trends

This paper examines long-term changes in the structure and composition of the groundfish species assemblage in three regions of the north-western North Sea. Scottish fisheries research vessel data collected during the months July-September over the period 1929-53 are compared with more recent August groundfish survey data covering the period 1980-93. Trends in the whole groundfish assemblage, and in a subset of the assemblage that is not targeted by commercial fisheries, are described. Long-term differences in species assemblage were subtle, and were most apparent in the dominance structure. Species diversity in the whole groundfish assemblage was marginally greater in the period 1929-53, but no difference was apparent within the non-target species assemblage. For the whole groundfish assemblage, diversity was greatest in the inshore region and least in the offshore area, but there was no obvious spatial gradient for the non-target species assemblage. Multivariate analyses indicated long-term changes and between-area differences in the species composition for both the whole groundfish assemblage and the non-target species subset. More detailed examination of the data revealed that the long-term changes resulted from relatively small and subtle differences in the relative abundance of rarer species, such as grey gurnard Eutrigla gurnardus (L.) and spur-dog Squalus acanthius L.. In contrast, changes in the relative abundance of the more common species, such as Norway pout Trisopterus esmarkii (Nilsson) and whiting Merlangius merlangus (L.), explained much of the between-area variation. Examination of species aggregated length-frequency distributions suggested that by the 1980s there had been a shift towards assemblages in which smaller fish were more highly represented. This was only apparent, however, in the whole groundfish species assemblage ; the length-frequency distributions of non-targeted species were almost identical in the two time periods. Overall, the results suggest that, although differences in the structure of the whole fish assemblage can be detected, the non-target groundfish assemblage appears to have remained relatively unchanged, despite a century of intensive fishing activity.

Physical Disturbance and Marine Benthic Communities: The Effects of Mechanical Harvesting of Cockles on Non-Target Benthic Infauna

1. The effects of physical disturbance processes on marine benthic communities remain an issue of considerable theoretical and practical importance, particularly with respect to the impact of fisheries activity and possible conflict with wildlife conservation objectives. One area where particular concern has been raised is with respect to the effects of mechanical harvesting of cockles (Cerastoderma edule) on non-target benthic infauna in intertidal communities. 2. This paper describes the results of manipulative field experiments which examine the effects of disturbance by two mechanical cockle harvesting methods, hydraulic suction dredging and tractor dredging. 3. Although the suction dredge experiment revealed some statistically significant effects, taken as a whole the results indicated that the faunal structure in disturbed plots recovered (i.e. approached that of the un-disturbed controls) by 56 days. This occurred against a background of consistent increases in the abundance of many taxa in both treatments, which we interpret as the normal seasonal response of the community. 4. The tractor dredge experiment revealed fewer statistically significant effects than the suction dredge experiment, and recovery from disturbance occurred against a background of general seasonal decline in the abundance of the fauna. From the available evidence the most likely mechanism of recovery was through the immigration of adults into disturbed areas. 5. We conclude that mechanical harvesting methods impose high levels of mortality on nontarget benthic fauna, but that recovery of disturbed sites is rapid and the overall effects on populations is probably low. Although our results suggest that tractor dredging has less effect than suction dredging, this result is most likely to be a consequence of the different times of year in which the experiments were conducted. Thus, for this location, we do not believe that a distinction can be made between the effects of the two methods. Although experimental manipulations cannot be conducted on comparable spatial scales to real fishing activity, we believe these results probably do not represent a major under-estimate of recovery times for intertidal habitats similar to the one chosen for this study.

A viable herd of genetically uniform cattle.

Inbreeding, which can lead to the loss of genetic variation or the accumulation of deleterious alleles, has been shown to reduce fitness in wild, zoo, laboratory and farmed animals. But it has been proposed that when combined with selection, inbreeding may purge deleterious alleles. Here we provide support for this hypothesis in a study of the Chillingham cattle, which shows that this viable herd is almost genetically uniform. The homozygosity of this herd far exceeds that of other cattle and that found in wild populations of other mammalian species.

Effects of vehicle movements during transport on the stress responses and meat quality of sheep

Two groups of 26 lambs were transported for 15 hours either on smooth highways or on rougher secondary roads. Nine of the animals in each group were monitored for heart rate and the plasma levels of cortisol, creatine kinase and lactate dehydrogenase, before the journey began, after four, eight and 12 hours and at slaughter. The pH of the meat was measured 45 minutes and 24 hours postmortem and its colour was assessed 24 hours postmortem. The lambs transported on smooth roads had a lower heart rate and lower plasma cortisol concentrations after eight and 12 hours than the lambs transported on rougher roads. Twenty-four hours after slaughter the pH of the meat of the lambs transported on smooth roads was lower than that of the lambs transported on rougher roads.

Canine epilepsy: a genetic counselling programme for keeshonds.

The predisposition of keeshonds (Dutch barge dogs) to an idiopathic epilepsy appears to be determined by a single autosomal recessive gene. The pedigrees of 15 litters which included animals diagnosed as epileptic (‘fitters’) were compared with those of 34 contemporary, normal animals. The pedigrees of all the fitters traced back, on both the paternal and maternal sides, to a common ancestor. Subsequently, further pedigrees and details of litters were gathered. If both parents of a fitter were heterozygous (‘carriers’), the progeny (120 in number) of all known carrier x carrier matings would be expected to have a ratio of three phenotypically normal animals to one fitter, that is, 90:30. The ratio observed (91:29) was not significantly different. The Keeshond Club has published a list from which the identities of carriers can be inferred, with the intention that known carriers should be excluded from breeding. A genetic counselling programme has been in operation since 1989, which is based on advising breeders on the probability that the offspring of proposed matings would be fitters or carriers; advice has been given on 77 proposed matings. The mean probability that the proposed matings would result in carriers has declined significantly, and this is consistent with a decline in the frequency of the gene for this form of epilepsy in the breed.

The role of the predatory crab, Liocarcinus depurator, in a marine food web

SUMMARY (2) Cages covering 1 m2 maintained crab densities from zero to eight crabs m-2 (0-32 times natural densities) for a period of 24 days. The total number of prey individuals, the number of species in samples and abundance of selected species were compared between treatments using ANOVA. Overall differences in assemblages were explored using multidimensional scaling. Effects on population size structure for four common species were also examined. (3) Contrary to expectation, there was little evidence that predation by Liocarcinus had any significant effect on the abundance of benthic species. The number of species in samples and the total number of individuals in samples were not significantly different between treatments and there were no effects on individual species which could be interpreted in terms of predation. The multivariate analysis, however, suggested some effects of caging, possibly due to the exclusion of other predators in addition to crabs in the case of infauna.

Pit-digging by the crab Cancer pagurus: a test for long-term, large-scale effects on infaunal community structure

1. Most studies which investigate the effects of predator disturbance on marine subtidal community structure focus on a scale appropriate to the individual disturbance event. Dramatic events are often observed at this local scale and it is tempting to infer that such disturbances are important at the landscape scale. For the more detailed small-scale studies, such conclusions are usually based on estimates of the rates of disturbance and recovery of individual patches. We argue that such calculations provide only weak tests of importance at the landscape scale and that manipulative field experiments offer much stronger tests

CHILLINGHAM PARK AND ITS HERD OF WHITE CATTLE: RELATIONSHIPS BETWEEN VEGETATION CLASSES AND PATTERNS OF RANGE USE

(1) Chillingham Park is a 134-ha tract of woodland and permanent grassland in northern England, grazed by a herd of white cattle. Indicator species analysis defined sixteen vegetation classes. (2) Bulls 4 or more years old shared home ranges, stable from year to year. The most dominant bull had the home range with the largest area of good grazing. (3) The size, botanical composition and location of the home ranges of the other bulls were not explicable purely in terms of social status. (4) The cattle used the different vegetation classes in a similar fashion from year to year, certain classes being favoured and others avoided. In spring, late autumn and winter, cows differed markedly from calves in their use of the various vegetation classes. (5) Indicator species analysis characterized Chillingham Park in a manner useful for ecological interpretation of patterns of behaviour of these cattle. This is believed to be its first application in a study of ungulate ecology.

Stress responses of sheep to routine procedures: changes in plasma concentrations of vasopressin, oxytocin and cortisol.

Putative immunodeficiency of weimeraner dogs in the UK A YOUNG weimeraner dog suffered recurrent disease of the alimentary tract, joints, skin and peripheral lymph nodes, central nervous system and conjunctivae during its first year of life. It had a left shift neutrophilia during periods of active disease and persistently low levels of serum IgG (2-8 to 9-2 mg/ml) and IgA (>0.1 to 0.26 mg/ml) in the absence of circulating immune complexes. One littermate died suddenly at 27 weeks of age and a second had an episode of pyoderma; both these dogs had low IgG (3-5 to 7-2 mg/ml) and the second had low IgA (<0-1 to 0.15 mg/ml). The dam of the litter and three related dogs also had low serum IgA (0-22 to 0.31 mg/ml) and no immune complexes were recorded in any of them. This is the first case of a putative immunodeficiency of weimeraners in the UK. DAY, M. J., POWER, C., OLESHKO, J. & ROSE, M. (1997) Journal of Small Animal Practice 38, 31 1 Field study of inactivated equine rotavirus vaccine OVER 300 pregnant thoroughbred mares were used in a two-year trial of an inactivated rotavirus vaccine. In the first year, the mares received intramuscular doses at eight, nine and 10 months of gestation, either of the vaccine or of a placebo; in the second year the previously vaccinated mares received a booster dose of the vaccine approximately a month before foaling. No adverse reactions were observed and the titres of antibodies were significantly higher in the vaccinated mares at foaling and 35 days later, and in the foals of the vaccinated mares for 90 days after birth. The severity and incidence of rotaviral diarrhoea were lower in the foals born to the vaccinated mares, but the differences were not statistically significant. POWELL, D. G., DWYER, R. M., TRAUB-DARGATZ, J. L., FULKER, R. H., WHALEN, J. W., SRINIVASAPPA, J., ACREE, W. M. & CHU, H. J. (1997) Journal of the American Veterinary Medical Association 211, 193 93

Rare and minority British sheep for meat production: the Shropshire and Ryeland as sires, and the Cotswold and primitive breeds as dams.

Abstract Two groups of comparisons were made between rare and minority British breeds of sheep, and numerically stronger genotypes. In the sire breed trial, Shropshire ( n =5) and Ryeland ( n =4) rams were compared as sires of meat lambs with Suffolk, Oxford Down, Texel and Dorset Down rams at two farms (total lambs marketed: n =732). At the first farm, lambs sired by the Ryeland and the Shropshire made poorer prices than those sired by the Suffolk and Oxford Down, because of small size and low price per kg respectively. At the second farm, the Ryeland and Dorset Down performed similarly in respect of days to slaughter, carcase weight and sale price. The Shropshire conferred rather poorer conformation on lambs than the Suffolk. In the maternal breeds trial, commercial crossbred (control) ewes ( n =84) and ewes of rare breeds (Cotswold n =10; and the primitive breeds Manx Loghtan n =17; Hebridean n =26; Shetland n =16) were mated with terminal sires on four farms. Lambs from Cotswolds reached slaughter condition earlier than control lambs, but were not as remunerative. Lambs from Hebrideans made a better price, per kg and per kg of ewe body weight, than control lambs from commercial crossbreds, but took longer to reach slaughter weight. Generally the primitive breeds produced lighter lambs but their production of lambs per unit of ewe body weight was no different from that of the commercial crossbreds. In this preliminary trial, economic advantages of using rare breeds were not demonstrated, but neither were there obvious economic penalties.