Distribution Of Search Effort Research Articles

Purse-seine vessels as platforms for monitoring the population status of dolphin species in the eastern tropical Pacific Ocean

In the eastern tropical Pacific Ocean, yellowfin tuna (Thunnus albacares) are often found in association with spotted (Stenella attenuata) and spinner (Stenella longirostris) dolphins. Purse-seine vessels use this co-occurrence to locate the tuna by searching for dolphins and associated birds. Data collected by onboard observers since the late 1970s were used to develop indices of relative abundance for dolphins, based on line-transect methodology, when the primary method of detection of dolphin herds was with binoculars. However, trend estimation was subsequently discontinued in 2000 due to concerns about changes in reporting rates of dolphin herd detections with increased use of helicopter and radar search. At present, as a result of a hiatus in fishery-independent surveys since 2006, fisheries observer data are the only source of information with which to monitor the status of eastern tropical Pacific Ocean dolphin populations. In this paper, trend estimation with the onboard observer data is revisited using a sightings-per-unit-effort approach. Despite different assumptions and model structure, the results indicate a lack of independence between the distribution of search effort and the search methods used, and the abundance of dolphin herds associated with tunas, on several spatial and temporal scales. This lack of independence poses a considerable challenge to the development of a reliable index of relative abundance for dolphins with these data. Given these results, alternatives for dolphin abundance estimation are discussed. One alternative is the use of purse-seine vessels for line-transect surveys during fishery closure periods. Another alternative is the use of purse-seine vessels during normal fishing operations as platforms for the collection of mark-recapture data (e.g., passive integrated transponder tags or genetics sampling). Life-history data collection, as a supplement to the collection of other data types, is also discussed. Further research and development is needed to assess whether these alternative methods will be useful.

A Caching Game with Infinitely Divisible Hidden Material

We consider a caching game in which a unit amount of infinitely divisible material is distributed among $n\geq 2$ locations. A Searcher chooses how to distribute his search effort $r$ about the locations so as to maximize the probability she will find a given minimum amount $\bar{m} =1-m\leq r$ of the material. If the search effort $y_{i}$ invested by the Searcher in a given location $i$ is at least as great as the amount of material $x_{i}$ located there she finds all of it, otherwise the amount she finds is only $y_{i}$. In other words she finds $\min \left\{ x_{i},y_{i}\right\} $ in location $i$. We seek the randomized distribution of search effort that maximizes the probability of success for the Searcher in the worst case, hence we model the problem as a zero-sum win-lose game between the Searcher and a malevolent Hider who wishes to keep more than $m$ of the material. We show that in the case $r=\bar{m}$ the game has a geometric interpretation that for $n=2$ corresponds to a problem posed by W. H. Ruckle in his monograph [Geometric Games and Their Applications, Pitman, Boston, 1983]. We give solutions for the geometric game when $n=3$ for certain values of $m$, and bounds on the value for other values of $m$. In the more general case $r\geq \bar{m}$ we show that for $n=2$ the game reduces to Ruckle's game

Optimal ambushing search for a moving target

This paper investigates a search problem for a moving target in which a searcher can anticipate the probabilities of routes selected by the target but does not have any time information about when the target transits the route. If the searcher had some time information, he could develop an efficient search plan by varying allocations of search effort based on time. Due to the lack of time information, the searcher must ambush the target by distributing search effort to places where the target is likely to pass. There are few papers that deal mathematically with this type of search problem with no time information. Employing the criterion of detection probability, we formulate the problem and obtain necessary and sufficient conditions for the optimal solution. By applying the conditions, we propose two methods for solving the problem. The convex programming problem can be easily solved numerically by some well-known methods, e.g. the gradient projection method or the multiplier method. By numerical comparison, it is verified that the proposed methods have the excellent performance in computational time. We also elucidate some properties of the optimal distribution of search effort by some numerical examples.

Effect of snow cover on seasonal changes in diet, habitat, and regional distribution of raptors that prey on small mammals in boreal zones of Fennoscandia

Seasonal changes in spatial distribution of search effort of birds that prey on small mammals were studied in two structurally different coniferous forest habitats in the northern boreal zone in SE Norway. During the season with snow cover both the proportion ofMicrotusrelative to that ofClethrionomysin the predators' diet, and their use of a clear‐cut relative to that of older forest were lower than during the snow‐free season. This was related to a lower relative availability of prey (Microtus agrestisandM. oeconomus) in the clear‐cut when the ground was snow‐covered than when it was snow‐free. Based on this local pattern I suggest the following explanation for differences in migratory strategy between raptors that prey on small mammals in Fennoscandian boreal zones: species that migrate to snow‐free areas in winter are either adapted to hunt by the energetically expensive method of quartering in open grassland habitats, where prey (Microtus) availability is relatively low during periods with snow cover (hen harrierCircus cyaneus, short‐eared owlAsio flammeus, and longeared owlA. otus), or by sit‐and‐wait in open grassland and forest habitats, the latter with relatively high prey availability during periods with snow cover, but unable to locate concealed prey (kestrelFalco tinnuculus, common buzzardButeo huteo, and roughlegged buzzardB. lagopus). In contrast, species that remain in areas with permanent snow cover during winter use the energetically cheap sit‐and‐wait tactic, and are able to hunt in closed forest habitat and localize concealed prey (the remaining owl species). Interspecific differences in prey availability as determined by hunting habitat and hunting mode is probably more important in shaping the migration patterns of Fennoscandian owls than is nest site availability.

Experimental studies on acarine predator–prey interactions: the distribution of search effort and the functional and numerical responses of predators in a patchy environment (Acarina: Phytoseiidae)

Laboratory experiments revealed that Phytoseiulus persimilis distributed its search effort in relation to prey density in a patchy environment, whereas Amblyseius degenerans distributed its search effort randomly among patches of prey. The main factor responsible for the aggregative response of P. persimilis was the length of its first visit to the patches. Although the functional responses of both predators changed with time, only those of P. persimilis closely reflected changes occurring in its distribution of search effort. The spatial complexity of the environment did not affect the overall predation rates of P. persimilis but it reduced its reproductive output. However, the predation rates of A. degenerans were adversely affected, suggesting that its fecundity would also be reduced in a spatially complex environment. Phytoseiulus persimilis distributed its progeny among patches containing relatively high prey densities and avoided ovipositing in the patch containing fewest prey. Neither species foraged optimally and possible reasons for this are discussed.

Experimental studies on acarine predator–prey interactions: distribution of search effort and predation rates of a predator population in a patchy environment (Acarina: Phytoseiidae)

The responses of a population of adult female Phytoseiulus persimilis and Amblyseius degenerans in a patchy environment were examined for 2 days in the laboratory. Progressive prey exploitation caused continuous redistribution of P. persimilis among the patches of prey, and although more individuals tended to occupy the highest density patch than other patches, there was an indication that "interference" limited the tendency of the predators to aggregate in this patch. In contrast, there was little redistribution of A. degenerans among the patches despite extensive prey exploitation. This species did not show an aggregative response nor was there any "interference" between the predators. The predation rates of P. persimilis declined with time and their foraging behaviour was not optimal on either day. In contrast, A. degenerans completely exploited the prey in all patches. The feeding and searching strategies of the two predator species are discussed in terms of their respective food habits. The implications of the characteristics of the predators for biological control are also briefly discussed.

The construction of an optimal distribution of search effort

AbstractSuppòse one object is hidden in the k‐th of n boxes with probability p(k). We know the probability q(t, k) of detecting the object if it is hidden in box k and we expend effort t searching box k. Our aim is to minimize the expected search effort of a successful search. Previously this problem has been solved only under the assumption that the functions q(·, k) are concave. We prove, without concavity assumptions, the existence of an optimal distribution of search effort and give a procedure for its construction.

Ovenbird (Aves: Parulidae) hunting behavior in a patchy environment: an experimental study

We investigated the foraging behavior of ovenbirds (Seiurus aurocapillus) in a patchy food supply. Nine birds were individually exposed on 2 successive days to four patches of 1.5 × 1.5 m containing 2, 4, 8, and 16 prey, respectively, in a 6 × 6 m field arena. Patch locations were kept constant; however, prey densities were interchanged on day 2.Amount of search path in patches increased exponentially with prey density. Birds rapidly shifted their search effort when prey densities were interchanged. Differential distribution of search effort resulted from more visits and greater search path per visit, owing to greater tortuosity of the search path in denser patches. Since less search path was required per prey found in denser patches, the search effort was concentrated in areas of high profitability and the birds took a higher percentage of prey available in these patches. However, in comparison with a simple model, their foraging among patches was suboptimal, except in the final period of day 1. Birds tended to avoid some recently visited patches although the overall sequence of visits to the four patches was random.It is proposed that differences in renewal and depletion rates of prey are important determinants of foraging behavior of ovenbirds and other species feeding in patchy environments.

Programmed Search in Adaptive Systems

An investigation is conducted of the programming of search by discrete data systems over a space volume. The distribution of search effort which leads to the greatest attainable information rate on a contact, or probability of its retention by maximizing the probability of a positive interrogation within some designated time interval is determined. An estimate of p, the relative frequency of positive interrogations of an individual contact, is utilized as a basis for adjustment of the sampling rate in accordance with results of the search program optimization study. It is shown that in the case of Rayleigh signal sources, the rate of convergence to a stable estimate of p is greatest if a search program characterized by a rapid sampling rate and a consequent low probability of detection on the individual trial is employed. If, following a sequence of observations, the statistical distribution of the position of the contact may be ascertained with some confidence, a suitably restricted space volume may be used in the allocation of search. It is shown that, if an extremal exists, the uniformly interrogated search field, which is optimal in the sense that the product of the containment and detection probabilities is greatest, is defined by an equiprobability density of location contour.