Journal of Experimental Marine Biology and Ecology 255 2000 175–186
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Effects of nearness to reef and exposure to sea-swell on estimates of relative abundance of Jasus verreauxi
H. Milne Edwards, 1851 recruits on collectors
S.S. Montgomery
NSW Fisheries , Fisheries Research Institute, P.O. Box 21, Cronulla, NSW, Australia 2230
Received 7 February 2000; received in revised form 14 August 2000; accepted 6 September 2000
Abstract
The hypothesis tested was that catches of J . verreauxi recruits numbers of pueruli to early
juveniles on sea-weed-type collectors were affected by the nearness of the collectors to vegetated reef and relative exposure of the collectors to sea-swell. Numbers of recruits on collectors set far
from reef were greater than on collectors near reef. Collectors far from reef may be the first, preferred type of habitat encountered by recruits as they move across the Continental Shelf.
Alternatively, fewer recruits may inhabit collectors set near reef because of the nearness of natural, vegetated reef. A cost–benefit analysis determined that the optimal sampling strategy for surveys
of the abundance of recruits at one location and time, would be three replicate collectors at each of three sites. Sampling once with this strategy at one location would give a standard error of around
20 of the mean. This information was used in developing a uniform and optimal methodology for full surveys to monitor the relative abundance of J
. verreauxi recruits along the coast of New South Wales.
2000 Elsevier Science B.V. All rights reserved.
Keywords : Lobster; Puerulus; Recruitment; Sampling strategy
1. Introduction
Data on the abundance of individuals in early stages of their life-history provide knowledge about recruitment to populations. One use of this information is in the
assessment of the impact of various managerial options on the population. In the case of spiny lobsters, the information is also used to predict the quantity of catch by the
commercial fishery in future years Phillips, 1986.
Tel.: 161-2-9527-8411; fax: 161-2-9527-8576. E-mail address
: montgomsfisheries.nsw.gov.au S.S. Montgomery. 0022-0981 00 – see front matter
2000 Elsevier Science B.V. All rights reserved.
P I I : S 0 0 2 2 - 0 9 8 1 0 0 0 0 2 9 1 - 4
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.S. Montgomery J. Exp. Mar. Biol. Ecol. 255 2000 175 –186
Scientists have commonly used the relative abundance of the puerulus stage in the life cycle of spiny lobsters as an index of recruitment to the population Booth and Phillips,
1994. Like studies on many other terrestrial e.g., Childers and Brecht, 1996; Maelzer et al., 1996 and aquatic e.g., Goldberg and Widman, 1989; Donaldson et al., 1991;
Killgore and Baker, 1996 organisms, a type of device specifically designed to catch pueruli has been used in studies of the relative abundance of spiny lobster populations
Phillips and Booth, 1994. Devices designed to catch pueruli have become commonly known as ‘collectors’ Phillips and Booth, 1994.
Surveys to measure the relative abundance of organisms should be uniform, unbiased, and optimal with respect to the quantity of the target species caught, and sufficiently
replicated in space and time to account for patchiness in distributions Kennelly et al., 1993. Pilot studies need to be done as a first step when developing a strategy for
sampling a population so that information is collected about i the effects of external factors on catches in sampling gear and ii the spatial and temporal heterogeneity in
distributions inherent in populations Snedecor and Cochran, 1967; Winer et al., 1991; Underwood, 1997. This information can be used in cost–benefit analyses to determine
optimal levels of replication in stratified, random surveys and allow a priori decisions to be made about the level of precision that is required around mean estimates of relative
abundance. These techniques have been used successfully in studying terrestrial Robinette et al., 1974; Caughley et al., 1976 and marine Kennelly and Underwood,
1984; Kennelly, 1989; Kennelly et al., 1993 communities. But, despite the number of studies that have used collectors to study patterns in the relative abundance of pueruli of
palinurids, there is little in the peer-reviewed literature about how external factors affect catches of spiny lobster recruits on collectors but see Cruz et al., 1991; Herrnkind and
Butler, 1994; Phillips and Booth, 1994 or about pilot studies and cost–benefit analyses done to optimise sampling design.
One factor that may affect catches of pueruli on collectors is the position of the collector in relation to its place in the water column, its nearness to reef and its exposure
to sea-swells. For instance, some of the greatest catches of Panulirus argus pueruli Latreille, 1804 have been taken from collectors set near the fringe of outer reefs, or the
oceanic side of bays and inlets Cruz et al., 1991; Herrnkind and Butler, 1994, whilst Phillips and Booth 1994 reported that catch rates of pueruli on collectors may be lower
where ‘‘there is an abundance of natural settlement substrate’’.
The spiny lobster J . verreauxi H. Milne Edwards, 1851, commonly called the
eastern rock or packhorse lobster, occurs in waters off the east coast of Australia Fig. 1 and also off New Zealand Kensler, 1967. The species is considered in New South
Wales to be a ‘botique’ seafood and supports a commercial trap fishery with a current Total Allowable Commercial Catch of 150 t, worth approximately 5 million.
Little is known about the life-cycle of J . verreauxi off New South Wales, but from
what is known for a review, see Montgomery, 1998, the species has a life-cycle similar to that of other shallow water palinurids e.g., Phillips et al., 1980. Females spawn in
waters shallower than 100 m Montgomery, 1992, then phyllosome larvae Kittaka, 1994a,b are transported to waters off the Continental Shelf Booth, 1986; MacWilliam
and Phillips, 1987. Nine to 12 months after hatching, individuals metamorphose from
S .S. Montgomery J. Exp. Mar. Biol. Ecol. 255 2000 175 –186
177
Fig. 1. Locations of sites used to investigate the effects of proximity to reef and exposure to sea-swell on catches of J
. verreauxi recruits. The small map shows the distribution of J. verreauxi off Australia and the study area.
the phyllosome stage to a puerulus, probably near the outer edge of the Continental Shelf, and then actively move toward shore Montgomery and Kittaka, 1994.
This paper is part of a study to develop a sampling strategy to monitor the effects of recent managerial decisions aimed at increasing the size of the J
. verreauxi population off New South Wales Montgomery, 1998. In order to design a sampling strategy to
collect information about the relative abundance of J . verreauxi recruits, I did pilot
studies to ascertain the effects of various factors on catches of the collectors. Montgomery and Craig 1997 compared the effects of different designs of collectors on
catches of J . verreauxi recruits and found that sea-weed-type collectors set near the
surface were best. This paper describes an experiment that was done to test the
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.S. Montgomery J. Exp. Mar. Biol. Ecol. 255 2000 175 –186
hypothesis that catches of J . verreauxi recruits will be greater on collectors set far from
natural reef than on collectors set near reef. Collectors set far from reef would be the only piece of preferred habitat in the vicinity, available to the recruits. So, those animals
that encounter the collector and choose to stay would have no other area of preferred habitat available to them. In contrast, collectors set near reef would be part of a greater
area of habitat for recruits to settle and perhaps move within. It follows from this reasoning that the number of recruits on collectors set far from reef would be expected
to be greater than on those near reef. I also present cost–benefit analyses on data from the experiment to determine the optimal numbers of collectors replicates and sites at
each location to use in future surveys.
2. Materials and methods
