Specific Life History Stages Research Articles

Habitat utilization by juvenile hawksbill turtles (Eretmochelys imbricata, Linnaeus, 1766) around a shallow water coral reef

Contemporary studies of sea turtle diving behaviour are generally based upon sophisticated techniques such as the attachment of time depth recorders. However, if the risks of misinterpretation are to be minimized, it is essential that electronic data are analysed in the light of first-hand observations. To this aim, we set out to make observations of juvenile hawksbill turtles (Eretmochelys imbricata, Linnaeus, 1766) foraging and resting in a shallow water coral reef habitat around the granitic Seychelles (4°'S, 55°'E). Data were collected from six study sites characterized by a shallow reef plateau (<5 m) and a flat sandy area at the base of the reef face (<10 m). Observation data were categorized into the following behaviours: (1) stationary foraging; (2) active foraging; (3) resting; and (4) assisted resting. Central to this investigation was the development of a technique for accurately estimating the size of sea turtles in situ based upon previously tested techniques for reef fishes. This revealed that through calibration, the curved carapace length (CCL) of marine turtles can be consistently estimated to within 10 cm of their actual size. Although rudimentary, this has advantages for assessing the residency or absence of specific life history stages from particular environments. Indeed, our data supported previous claims that following the reproductive season, adult hawksbills in the region may move away from the nesting beaches to alternative foraging grounds whilst immature turtles (following the pelagic juvenile stage) may opt to reside in areas close to their natal beaches. With regards to habitat utilization, juvenile hawksbills displayed an alternating pattern of short, shallow foraging dives followed by deeper, longer resting dives. These findings are consistent with previous electronic studies of free-range diving in this species and suggest that the maximization of resting duration may be an important factor driving this behaviour.

Tolerance to Acid Water Among Strains and Life Stages of Atlantic Salmon ( Salmo Salar L.)

Reintroduction of Atlantic salmon (Salmo salar L.) after liming of acidified barren salmon rivers could benefit by choosing acid tolerant strains. Testing different life history stages from fry to smolts of five salmon strains with different acidification history demonstrated strain-specific variation in tolerance to acid aluminum-rich waters for stages from fry to parr. Contrary to expectation, salmon from non-acidified rivers were more tolerant. Differences in sensitivity were found between life history stages. Within a specific life history stage, size-dependent sensitivity was found; small fish being more sensitive to pH while large fish were more sensitive to aluminum. Presmolts showed the same relative tolerance between strains as younger stages. These differences disappeared, however, when the smolt reached full smoltification, probably due to supersensitivity at this stage. Poor water quality during the last period of smoltification and outmigration can thus mask the genetic potential for tolerance to acidic rivers.

Early postlarval fish in the hyperbenthos of the Dutch Delta (south-west Netherlands)

Early (post)larval fish constitute a significant part of the temporary hyperbenthos, i.e. of the fauna living in the lower reaches of the water column close to the substratum. Information on the densities and spatial and temporal variations of these stages, as well as on their lengths at the moment of occurrence, can be an important contribution to the knowledge of their dispersion, migrations and to the identification of possible bottlenecks in their recruitment. Therefore the hyperbenthos of the Voordelta, a shallow coastal zone in front of the Dutch Delta, as well as that of the subtidal channels and the intertidal brackish marsh creeks of the Westerschelde Estuary, was sampled monthly during one year by means of a sledge and a stow net. A total of 37 taxa were recorded from 410 samples. Densities often exceeded 400 ind 1000 m−2 in the Voordelta and 300 ind 1000 m−2 in the Westerschelde, including the tidal marshes of Waarde and Saeftinghe. The dominant taxa were clupeid larvae (predominantly herring Clupea harengus and sprat Sprattus sprattus), Pomatoschistus spp. (a mixture of sand goby P. minutus and Lozano's goby P. lozanoi), common goby Pomatoschistus microps, Syngnathus spp. (probably almost exclusively Nilsson's pipefish S.rostellatus), plaice Pleuronectes platessa, sole Solea solea and flounder Pleuronectes flesus. Most species were found at a larger size in the Westerschelde (and in the tidal marshes) suggesting migration from the shallow coastal area into the estuary. Several species utilize the tidal marshes in the brackish reaches of the Westerschelde. The nursery value of these areas however, is restricted to specific early life history stages of a few species, especially flounder, bass Dicentrarchus labrax and the common goby. The estuary itself seems to function as a nursery for other species like sole and plaice. The hyperbenthic sledge was found to sample specific life history stages of postlarval flatfish (early settlement stages at the onset of asymmetry), which are not easy to sample with other types of sampling gear.

Factors Affecting Phenology in a Temperate Insect Community

Phenology of 117 species of butterflies and skippers of a Rocky Mountain foothills community are examined, emphasizing the factors producing phenological patterns. Medians and interquartile ranges are calculated, from 2 decades of species-day-collector records, for each adult flight. Sixty-seven percent of the 111 native species have only one generation per year, 4% have one and a partial second, 15% have two, and 15% have three or more. Average date of adult flight depends mostly on the life history stage of the overwintering animals (adult overwinterers fly in early spring, followed chronologically by pupal, larval and finally egg overwinterers), and also depends on the larval growth rate as affected by the host plant (flower/fruit feeders fly earliest, then herb leaf feeders, shrub/tree leaf feeders, and finally grass/sedge feeders). Winter does not decrease the spread (synchrony) of the adult flights of insects that overwinter in a single life history stage: the data form a bowl shape-, with average duration of the flights longest in the spring, short or long in midsummer and fairly long in late summer. The best explanation of the bowl shape involves spring/autumn weather, especially alternating hot/cold fronts, increased microclimate differences between Nand S-facing slopes and longer life span in cool weather, and perhaps, also concerns the long-term selective advantage of spreading the risk of emerging at one time in spring or autumn when a freeze can decimate all the highly synchronized emerging adults. Midsummer species may have active (photoperiodic?) mechanisms to synchronize their flights. Flower/fruit feeders tend to overwinter as pupae and to have only one yearly flight. Little larval feeding occurs in late summer, mostly by comparatively mobile polyphagous species having several generations. INTRODUCTION Phenology is the study of the relationship between weather and periodic biological phenomena. Temperate insect faunas consist of a seasonal progression of the appearance of different species. The appearance of a species is usually short and is keyed to a specific time during the growing season, and each species usually has a specific life history stage in which it overwinters. Tauber and Tauber (1976), Denno and Dingle (1981), Brown and Hodek (1983) and Lieth (1974) review insect phenology in general. Many papers have charted the seasonal progression of butterfly species (e.g., Yamamoto, 1974, 1976, 1977), but few have attempted to elucidate the mechanisms causing these patterns (Shapiro, 1975a). We first present the theory of mechanisms influencing time of appearance and duration of each adult flight, and the number of generations per species per season, in a temperate environment. We then examine the butterflies of Red Rocks Park in the Rocky Mountain foothills to determine which of these factors affect phenology in nature. The average date of appearance of adults and average duration of adult flight are reported for each species by use of medians and interquartile ranges of the species-date-collector records. In our attempt to uncover the mechanisms, both proximal (physiological) and evolutionary, for phenological patterns, we have dissected the temporal components of an adult generation, and have used the overwintering stage, the adult life span, time of development, alternating

Application of a Polynomial Distributed Lag Model to the Maine Lobster Fishery

Time series data on catch and effort for the American lobster (Homarus americanus) from the state of Maine during the period 1933 to 1974, as well as mean annual sea surface temperatures for the same period were examined by means of a polynomial distributed lag model. The model was described and shown to be sufficiently flexible to take into account environmental influences over specific life history stages as well as over the entire life history of the species. The significance of lagged temperature effects and the fit of the model to the observed data were demonstrated.