Movement and habitat use by the marbled lungfish Protopterus aethiopicus Heckel 1851 in Lake Baringo, Kenya

The marbled lungfish, Protopterus aethiopicus, a recent introduction into Lake Baringo, Kenya is now an important commercial species there. Because little is known about its behaviour, we used ultrasonic telemetry to investigate its movements and use of habitat as part of a broader biological study. Twelve marbled lungfish were implanted with ultrasonic tags and tracked for variable periods between September 2001 and 2002. Two individuals were tracked for most of the study period. Daily movement ranged from little or none to 5.2 km. Mean hourly rates of movement for three fish located twice a day (morning and late afternoon) over several days suggested that individuals were active throughout the diel period. Maximum lake depth was about 3 m and fish utilized all depths greater than 1 m. Six home ranges described for four lungfish varied in size from 5.8 to 19.8 km ² and were occupied for between 2 and 4.5 months. Use of habitat and the movement of marbled lungfish in Lake Baringo appeared to be influenced more by biotic than abiotic factors.     

Space Utilization and Swimming Depth of White Sharks, Carcharodon carcharias, at the South Farallon Islands, Central California

This paper presents information on the movements of white sharks, Carcharodon carcharias, at the South Farallon Islands (SFI), central California. Acoustic telemetry techniques provided preliminary data on the diurnal space utilization, movement patterns and swimming depths of four white sharks, ranging from approximately 3.7 to 4.9m in length. Sharks swam within about 10m of the bottom to depths of approximately 30m, but in deeper water they tended to stray more from the bottom. Activity spaces for time periods tracked ranged from 1.84 to 9.15km². Indications are that an inverse relationship exists between length and activity space. During the time tracked, larger individuals swam within particular areas around the islands whereas smaller individuals did not restrict their movements in the same manner. Values of a site attachment index were inversely related to length for all sharks tracked. The site attachment indices, apparent inverse relationship between total length and activity space and observations on telemetered and other known individuals support a hypothesis that larger sharks possess site fidelity in their search for prey at SFI, within and between years. With the high frequency of predation by white sharks on juvenile northern elephant seals at SFI in the fall, the majority of the sharks' movements are probably related to their search for these pinniped prey. These data provide preliminary evidence that white sharks at SFI may search for prey by swimming in a particular area over a number of days or weeks, traversing the area in a manner which maximizes coverage, and swimming close to the bottom or at a distance far enough from the surface to remain cryptic from prey.     

Population spatial structuring on the feeding grounds in North Atlantic humpback whales (Megaptera novaeangliae)

Population spatial structuring among North Atlantic humpback whales Megaptera novaeangliae on the summer feeding grounds was investigated using movement patterns of identified individuals. We analysed the results from an intensive 2-year ocean-basin-scale investigation resulting in 1658 individuals identified by natural markings and 751 individuals by genetic markers supplemented with data from a long-term collaborative study with 3063 individuals identified by natural markings. Re-sighting distances ranged from <1 km to >2200 km. The frequencies ( F ) of re-sighting distances ( D ) observed in consecutive years were best modelled by an inverse allometric function ( F =6631 D ^−1.24, r ²=0.984), reflecting high levels of site fidelity (median re-sighting distance <40 km) with occasional long-distance movement (5% of re-sightings >550 km). The distribution of re-sighting distances differed east and west of 45°W, with more long-distance movement in the east. This difference is consistent with regional patterns of prey distribution and predictability. Four feeding aggregations were identified: the Gulf of Maine, eastern Canada, West Greenland and the eastern North Atlantic. There was an exchange rate of 0.98% between the western feeding aggregations. The prevalence of long-distance movement in the east made delineation of possible additional feeding aggregations less clear. Limited exchange between sites separated by as little as tens of kilometres produced lower-level structuring within all feeding aggregations. Regional and temporal differences in movement patterns reflected similar foraging responses to varying patterns of prey availability and predictability. A negative relationship was shown between relative abundance of herring and sand lance in the Gulf of Maine and humpback whale movement from the Gulf of Maine to eastern Canada.     

Short-term Movements of Juvenile and Neonate Sandbar Sharks, Carcharhinus plumbeus, on their Nursery Grounds in Delaware Bay

We investigated short-term movements of neonate and juvenile sandbar sharks, Carcharhinus plumbeus, on their nursery grounds in Delaware Bay. The majority of sharks tracked limited their movements to water less than 5m deep, remained within 5km of the coastline, and occupied oblong activity spaces along the coast. In addition to site-attached coastal movements observed, several sharks moved entirely across Delaware Bay or spent considerable time in deeper portions of the central bay. Sharks tracked on the New Jersey side of the bay tended to spend more time in deeper water, farther from shore than sharks tracked on the Delaware side. Observation-area curves estimated that optimal tracking time for sandbar sharks in Delaware Bay was 41h. Indices of site attachment showed that movement patterns of tracked sandbar sharks varied from nomadic to home ranging. There was no significant difference in rate of movement for day/night, crepuscular periods, or between juveniles and neonates. In general, young sandbar sharks patrolled the coast and appeared to be site attached to some extent, but were capable of making longer excursions, including movement entirely across Delaware Bay.     

An acoustic telemetry study of seabream (Sparus aurata L.): first results on activity rhythm,effects of environmental variables and space utilization

The movements of seabream (Sparus aurata L) were recorded in two earthen ponds (250 m² and 400 m²) by tracking fish tagged with miniature acoustic transmitters. Five seabreams, 500 g in weight, were tracked for periods of four or five days. Fish positions were recorded continuously using an acoustic telemetry system. Each of the five tagged seabreams were tracked individually. Two fishes were released schooled with numerous other individuals, two others were released in isolation and one was grouped with three other individuals.The schooled seabreams were more active in general and, in the large school they were diurnal; isolated fishes however, were more active at night. Temperature influences significantly and progressively the fish activity. Activity decreases at night and increases during daylight. Oxygen saturation also influences swimming activity with a general positive relationship.The horizontal distribution of this species was not uniform. Its resting area was generally located around some particular landmarks such as inlet or outlet pipes in the ponds. No feverish feeding competition was observed between individuals of the same school. The feeding area was cleaned rapidly, in less than 10 minutes, without subsequent returns from the resting area to the feeding area.

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Résumé Les déplacements de la daurade (Sparus aurata L.) ont été enregistrés dans deux bassins en terre (250 m² et 400 m²) en suivant des poissons marqués avec des émetteurs acoustiques miniaturisés. Cinq daurades d'un poids individuel de 500 g furent suivies durant des périodes de 4 ou 5 jours. Les positions des poissons ont été enregistrées en continu avec un systéme de télémétrie acoustique. Chacun des cinq poissons marqués fut suivi individuellement. Deux poissons furent regroupés avec de nombreux autres individus, deux autres furent laissés seuls et le dernier fut mis avec trois autres individus.Les daurades groupées étaient en général plus actives et, en grand banc, étaient diurnes; les poissons isolés étaient toutefois plus actifs durant la nuit. La température influence significativement et progressivement l'activité des poissons. L'activité décroît durant la nuit et augmente pendant le jour. Le pourcentage de saturation en oxygéne agit aussi, de façon positive, sur l'activité de nage.La distribution horizontale de cette espéce n'est pas uniforme. Son aire de repos est généralement localisée dans quelques zones particuliéres comme les arrivées et les sorties d'eau. Aucune compétition alimentaire fébrile n'a été observée entre les individus d'un même banc. L'aire de nourrissage est rapidement nettoyée, en moins de 10 minutes, sans retours ultérieurs depuis la zone de repos jusqu' à la zone de nourrissage.

     

Effects of sampling regime on the mean and variance of home range size estimates

1. Although the home range is a fundamental ecological concept, there is considerable debate over how it is best measured. There is a substantial literature concerning the precision and accuracy of all commonly used home range estimation methods; however, there has been considerably less work concerning how estimates vary with sampling regime, and how this affects statistical inferences. 2. We propose a new procedure, based on a variance components analysis using generalized mixed effects models to examine how estimates vary with sampling regime. 3. To demonstrate the method we analyse data from one study of 32 individually marked roe deer and another study of 21 individually marked kestrels. We subsampled these data to simulate increasingly less intense sampling regimes, and compared the performance of two kernel density estimation (KDE) methods, of the minimum convex polygon (MCP) and of the bivariate ellipse methods. 4. Variation between individuals and study areas contributed most to the total variance in home range size. Contrary to recent concerns over reliability, both KDE methods were remarkably efficient, robust and unbiased: 10 fixes per month, if collected over a standardized number of days, were sufficient for accurate estimates of home range size. However, the commonly used 95% isopleth should be avoided; we recommend using isopleths between 90 and 50%. 5. Using the same number of fixes does not guarantee unbiased home range estimates: statistical inferences differ with the number of days sampled, even if using KDE methods. 6. The MCP method was highly inefficient and results were subject to considerable and unpredictable biases. The bivariate ellipse was not the most reliable method at low sample sizes. 7. We conclude that effort should be directed at marking more individuals monitored over long periods at the expense of the sampling rate per individual. Statistical results are reliable only if the whole sampling regime is standardized. We derive practical guidelines for field studies and data analysis.