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1.
The Great Bay Estuary, New Hampshire, USA is near the northern distribution limit of the American horseshoe crab (Limulus polyphemus). This estuary has few ideal beaches for spawning, yet it supports a modest population of horseshoe crabs. There is no organized monitoring program in the Great Bay Estuary, so it is unclear when and where spawning occurs. In this 2-year study (May through June, 2012 and 2013), >5,000 adult horseshoe crabs were counted at four sites in the estuary. The greatest densities of horseshoe crabs were observed at Great Bay sites in the upper, warmer reaches of the estuary. Peaks of spawning activity were not strongly correlated with the times of the new or full moons, and similar numbers of horseshoe crabs were observed mating during daytime and nighttime high tides. While many environmental factors are likely to influence the temporal and spatial patterns of spawning in this estuary, temperature appears to have the most profound impact. 相似文献
2.
David R. Smith 《Estuaries and Coasts》2007,30(2):287-295
Because the Delaware Bay horseshoe crab (Limulus polyphemus) population is managed to provide for dependent species, such as migratory shorebirds, there is a need to understand the
process of egg exhumation and to predict eggs available to foraging shorebirds. A simple spatial model was used to simulate
horseshoe crab spawning that would occur on a typical Delaware Bay beach during spring tide cycles to quantify density-dependent
nest disturbance. At least 20% of nests and eggs were disturbed for levels of spawning greater than one third of the average
density in Delaware Bay during 2004. Nest disturbance increased approximately linearly as spawning density increased from
one half to twice the 2004 level. As spawning density increased further, the percentage of eggs that were disturbed reached
an asymptote of 70% for densities up to 10 times the density in 2004. Nest disturbance was heaviest in the mid beach zone.
Nest disturbance precedes entrainment and begins the process of exhumation of eggs to surface sediments. Model predictions
were combined with observations from egg surveys to estimate a snap-shot exhumation rate of 5–9% of disturbed eggs. Because
an unknown quantity of eggs were exhumed and removed from the beach prior to the survey, cumulative exhumation rate was likely
to have been higher than the snap-shot estimate. Because egg exhumation is density-dependent, in addition to managing for
a high population size, identification and conservation of beaches where spawning horseshoe crabs concentrate in high densities
(i.e., hot spots) are important steps toward providing a reliable food supply for migratory shorebirds. 相似文献
3.
Andrew McGowan 《Estuaries and Coasts》2018,41(7):2120-2127
The Delaware Bay region is the epicenter of horseshoe crab, Limulus polyphemus, activity, and despite the ecological and commercial importance of this species, few studies have examined the long-term movements of horseshoe crabs in this area and the amount of mixing that takes place between smaller coastal embayments within the region and the Delaware Bay proper, factors that are critical to effective management. To better understand these factors, 5568 crabs were tagged in the Delaware Inland Bays as part of the U.S. Fish and Wildlife Service’s (USFWS) Cooperative Horseshoe Crab Tagging Program in 2002–2016. A high re-sight rate of 20.1% (1123 crabs) was reported to the USFWS. Re-sights suggest that the Delaware Bay population is distributed between coastal New Jersey (south of Barnegat Bay) and coastal Virginia (north of Chincoteague Inlet). There were 90 re-sights in the Inland Bays and 148 re-sights in Delaware Bay, with 320 days or more between tagging and re-sight, showing that substantial interchange between successive spawning seasons occurs. Distance analyses demonstrated that crabs can move between the Inland Bays and other Delaware Bay region waterbodies within a single year. The findings of this study support the current management strategy of splitting the harvest of Delaware Bay crabs between New Jersey, Delaware, Maryland, and Virginia and also demonstrate that the waterbodies within the Delaware Bay region are highly connected. This connectivity supports protecting spawning habitat within the smaller embayments of the Delaware Bay region and including spawning surveys from these systems in future stock assessments. 相似文献
4.
Mark L. Botton Robert E. Loveland John T. Tanacredi Tomio Itow 《Estuaries and Coasts》2006,29(5):820-830
We assessed the suitability of intertidal habitats for spawning by horseshoe crabs (Limulus polyphemus) at 12 proposed restoration sites identified by the United States Army Corps of Engineers along the shore of Jamaica Bay,
a highly developed estuary in New York City. Based on beach geomorphology, we chose to quantify horseshoe crab activity at
five of the sites during the May–July 2000 breeding season. Horseshoe crabs spawned intensively on small patches of suitable
sand within larger areas of eroding shoreline with bulkheads and rubble fill. Small areas of sand behind grounded barges at
Brant Point and Dubos Point had densities of over 100,000 eggs m−2, which was equal to or greater than the egg densities on longer, more natural appearing beaches at Spring Creek and Dead
Horse Bay, or at a sand spit at Bayswater State Park. There were no significant differences in the percentage of Jamaica Bay
horseshoe crab eggs that completed development when cultured using water from Jamaica Bay or lower Delaware Bay, a less polluted
location. Only 1% of the embryos from Jamaica Bay exhibited developmental anomalies, a frequency comparable to a previously
studied population from Delaware Bay. We suggest that the distribution and abundance of horseshoe crabs at our study areas
in Jamaica Bay is presently limited by the availability of suitable shoreline for breeding, rather than by water quality.
Restoration efforts that increase the amount of sandy beach in this urban estuary have a good likelihood of benefiting horseshoe
crabs and providing additional value to migrating shorebirds that use horseshoe crab eggs as food. 相似文献
5.
A contribution to the population biology of horseshoe crabs,Limulus polyphemus (L.), in Delaware Bay
The 1977 peak population of spawning horsehoe crabs,Limulus polyphemus, in Delaware Bay, was comprised of about 222,000 males and 51,000 females. This estimate, based upon a shoreline survey of spawning intensity along Delaware and New Jersey beaches at the time of full moon tides in June, was corroborated by a quantification of egg clusters in a beach. Fecundity of gravid females was used, in conjunction with the egg cluster estimate, to approximate the number of females responsible for the observed quantity of eggs. The present spawning population of Delaware Bay is several fold larger than that which existed during the 1960’s. From a longer historical perspective, however, the population is far from approaching the numbers and spawning intensity reported a century ago. 相似文献
6.
Anne Rudloe 《Estuaries and Coasts》1980,3(3):177-183
Breeding activity of the horseshoe crab,Limulus polyphemus, was quantitatively monitored in Apalachee Bay, Florida, throughout one breeding season. Breeding peaked at times of full and new moon at the hour of high tide. Breeding activity was heavier on night tides than on corresponding day tides of the same date. Males routinely outnumbered females and indications of sperm competition were present. Many horseshoe crabs buried in the intertidal zone throughout the subsequent low tide and returned to the beach to breed again on the following high tide. A tagging study of the horseshoe crab indicated that male animals return to breeding beaches more frequently than females. Most animals tagged at breeding beaches did not move away from the tagging site during a breeding season and were recovered at the point of release. No long-range movements were noted. The sex ratio of animals tagged near breeding beaches was predominately male while it was predominately female for animals collected and tagged 3–6 miles offshore. A nine percent recovery rate was achieved. Existing localized populations are potentially subject to depletion due to heavy collecting pressure on breeding beaches. 相似文献
7.
The Delaware Bay contains the world’s largest population of horseshoe crabs, which constitute an ecologically significant component of this estuarine ecosystem. The North Atlantic speciesLimulus polyphemus has an extensive geographical distribution, ranging from New England to the Gulf of Mexico. Recent assessments of the Delaware Bay population based on beach spawning and trawling data have suggested a considerable decrease in the number of adult animals since 1990. Considerable debate has centered on the accuracy of these estimates and their impact on marine fisheries management planning. Compounding this problem is the lack of information concerning the genetic structure of Atlantic horseshoe crab populations. This study assessed patterns of genetic variation within and between the horseshoe crab populations of Delaware Bay and Chesapeake Bay, using both Random Amplification of Polymorphic DNA (RAPD) and DNA sequence analysis of the mitochondrial cytochrome oxidase I gene (COI). We examined 41 animals from Delaware Bay and 14 animals from the eastern shore of Chesapeake Bay. To provide high quality, uncontaminated genomic DNA for RAPD analysis, DNA was isolated from hemocytes by direct cardiac puncture, purified by spin column chromatography, and quantified by agarose gel electrophoresis. RAPD fingerprints revealed a relative paucity of polymorphic fragments, with generally homogeneous banding patterns both within and between populations. DNA sequence analysis of 515 bases of the 5′ portion of the mitochondrial COI gene showed haplotype diversity in the Chesapeake Bay sample to be significantly higher than in the Delaware Bay sample, despite the larger size of the latter. Haplotype analysis indicates minimal contemporary gene flow between Delaware Bay and Chesapeake Bay crab populations, and further suggests that the Delaware Bay population is recovering from a recent population decline. 相似文献
8.
Influence of waves and horseshoe crab spawning on beach morphology and sediment grain-size characteristics on a sandy estuarine beach 总被引：2，自引：0，他引：2
The effects of wave action and horseshoe crab spawning on the topography and grain-size characteristics on the foreshore of an estuarine sand beach in Delaware Bay, New Jersey, USA were evaluated using data collected over six consecutive high tides. Data were gathered inside and outside a 25 m long exclosure constructed to create a control area free of disturbance by crabs. The density of crabs in the swash zone outside the exclosure was 8·1 organisms m−2. The maximum depth of sediment activation on the upper foreshore where spawning occurred was 0·103 m during periods characterized by low significant wave heights: < 0·08 m. This depth is greater than the depth of activation by waves alone during moderate significant wave heights of 0·16–0·18 m but less than the maximum depth (0·127 m) recorded when spawning occurred during periods of moderate wave heights. Spawning, combined with moderate wave heights, creates a concave upper foreshore that is similar to the type of profile change that occurs during storms, thus lowering the wave-energy threshold for morphological response. Spawning during low wave heights increases the mean grain size and sorting of surface sediments caused by the addition of gravel to the swash. Sedimentological differences are most pronounced on the upper foreshore, and data from this location may be most useful when using grain-size characteristics to interpret the effect of spawning in the sedimentary record. Depths of sediment reworking by horseshoe crabs can be greater than those by subsequent storm waves, so evidence of spawning can be preserved on non-eroding beaches. Greater depth of activation by horseshoe crab spawning than by waves alone, even during moderate-energy conditions, reveals the importance of crab burrowing in releasing eggs to the water column and making them available for shore birds. 相似文献
9.
Mark L. Botton Christina P. Colón John Rowden Susan Elbin Debra Kriensky Kim McKown Matthew Sclafani Robert Madden 《Estuaries and Coasts》2018,41(4):974-987
Restoration of horseshoe crab spawning habitats through beach nourishment may be considered as a potential strategy to enhance reproductive success in areas where estuarine beaches have been lost to coastal erosion and development. The US Army Corps of Engineers performed a beach nourishment project at Plumb Beach (Jamaica Bay, Brooklyn, NY) in 2012 to stabilize the shoreline. While the addition of sand was done to protect infrastructure, it created an opportunity to examine the responses of American horseshoe crabs (Limulus polyphemus) to beach nourishment using a BACI (before-after control impact) design. During Spring 2012, before beach nourishment, horseshoe crabs made minimal use of the highly degraded western section of Plumb Beach in comparison to a nearby reference site, as quantified by numbers of spawning adults at high tide and densities of horseshoe crab eggs in core samples. In the first post-nourishment field season (Spring 2013), there was no detectable increase in horseshoe crab spawning activity on the newly restored beach. In 2014 and 2015, the density of spawning females began to increase at the nourished beach, although their numbers and especially the density of horseshoe crab eggs remained much lower than at the reference site. Three years after beach nourishment, differences in sediments texture (mean grain diameter, percent gravel, sorting, skewness, and hardness) were still evident between the nourishment and reference sites. Our results suggest that (1) at this site, beach nourishment appeared to bring about only slow increases in horseshoe crab spawning density after several seasons and (2) subtle differences in beach geomorphology over relatively short distances can be detected by horseshoe crabs and may underlie their selection of specific nesting sites. 相似文献
10.
The distribution, abundance, and dispersal patterns of horseshoe crab (Limulus polyphemus) trilobite larvae were determined from 671 plankton tows taken near a spawning beach in lower Delaware Bay, New Jersey, in
1998 and 1999. In both years, peaks in larval abundance occurred during periods of rough surf (>30 cm wave heights). Planktonic
larvae were significantly more abundant nocturnally than during the day, but there was no evidence of a lunar component to
larval abundance. Larvae were strongly concentrated inshore; trilobites were 10–100 times more abundant in the immediate vicinity
of the shoreline than they were 100–200 m offshore. The strong tendency ofLimulus larvae to remain close to the beach suggests that their capability for long-range dispersal between estuaries is extremely
limited. We suggest that limited larval dispersal potential may help explain previously observed patterns of genetic variation
among the Mid-Atlantic horseshoe crab populations. 相似文献
11.
The objective of this simulation study was to create an age-structured population model for horseshoe crabs (Limulus polyphemus) in the Delaware Bay region using best available estimates of age-specific mortality and recent harvest levels. Density dependence
was incorporated using a spatial model relating egg mortality with abundance of spawning females. Combinations of annual female
harvest (0, 50, 100, and 200 thousand), timing of female harvest (before or after spawning), and three levels of density-dependent
egg mortality were simulated. The probability of the population increasing was high (>80%) with low and medium egg mortality
and harvest less than 200 thousand females per year. Under the high egg mortality case, the probability of the population
increasing was <50% regardless of harvest. Harvest occurring after spawning increased the probability of population growth.
The number of eggs available to shorebirds was highest when egg mortality was lowest and female abundance was at its highest
levels. Although harvest and egg mortality influenced population growth and food availability to shorebirds, sensitivity and
elasticity analyses showed that early-life stage mortality, age 0 mortality in particular, was the most important parameter
for population growth. Our modeling results indicate areas where further research is needed and suggest effective management
will involve a combination of harvest management and actions to increase early juvenile survival. 相似文献
12.
Atlantic horseshoe crabs,Limulus polyphemus, are currently harvested for biomedical, scientific, and bait purposes. In recent years, changes in population abundance
and magnitude of harvesting have raised concerns about the status of this resource. We found horseshoe crab harvest in Pleasant
Bay, Massachusetts, was selective by sex and size. Biomedical harvest preferred larger individuals and females, the scientific
harvest preferred smaller individuals and males, and the bait harvest preferred females. Total 2001 harvest for all purposes
accounted for the mortality of ∼1–2% the adult population. Biomedical harvest accounted for the greatest loss of horseshoe
crabs from Pleasant Bay, ∼1–1.6% of the total population. Although biomedical harvest had the lowest associated mortality
rate (∼10–15%), many more crabs were harvested from Pleasant Bay for biomedical purposes than for other uses. The scientific
harvest accounted for the mortality of ∼0.4% of the population, and bait harvest accounted for the smallest mortality at ∼0.06%
of the population. Harvest mortality rate was estimated to be lower in Pleasant Bay than in other Cape Cod areas and may be
lower than natural mortality in the population. This study is the first qualitative investigation of commercial harvest on
horseshoe crab populations and emphasizes that harvest pressures on different populations need to be individually evaluated. 相似文献
13.
B. L. Swan 《Estuaries and Coasts》2005,28(1):28-40
Adult horseshoe crabs,Limulus polyphemus, were tagged in the Middle Atlantic Bight area, from New York to Virginia on the continental shelf and within bays, to determine
their migratory patterns and longevity. Of 30,432 horreshoe crabs that were tagged during the years 1986–2002, 1,122 were
recovered alive, and 1,027 were dead. Many of the live recoveries were observed within 30 d (54.4%) and after years (37.53%)
with one tagged animal surviving up to 10 yr. In 9 locations from Great Kills Harbor, New York, to Chesapeake Bay, Maryland,
the horseshoe crabs return to their release beach within days during the spawning season. Of the 762 (100%) recoveries from
crabs released along the Delaware Bay shoreline, 75.07% traveled 0–20 km, 21.0% traveled 20–50 km, 2.36% traveled 50–100 km,
and 1.57% traveled over 100 km. Within Delaware Bay, 327 tagged animals (43.6%) had moved away from the release points to
other locations, and 59 of these had moved out of the bay onto the continental shelf along the Mid-Atlantic Bight coastline.
Horseshoe crabs migrate into Delaware Bay from waters off Ocean City, Maryland, and adjacent coastal bays. In addition to
defining the range of the Delaware Bay spawning populations, 2 neighboring populations were identified by the tagging program.
In one, animals tagged in southern New York mingled with those in the Sandy, Hook, New Jersey area, comprising a population
that ranged from Raritan Bay across New York Harbor to Jamaica Bay. The second confirmed that a discrete population existed
in northern Chesapeake Bay in the general vicinity of the Annapolis Bay Bridge. 相似文献
14.
Biological and physical reworking of sediments can profoundly affect the structure and functioning of benthic communities. The depth of the disturbance is an important factor that controls the types of organisms that can exist within the sediments. Large numbers of horseshoe crabs,Limulus polyphemus, spawn each spring on the sandy shores of Delaware Bay beaches. We have used this abundance peak to provide an estimate of the depth of sediment disruption caused by this species on an intertidal flat adjoining a major spawning beach. Vertical columns of marked sediment were placed in three locations of an intertidal flat. Some columns were protected with cages while others remained unprotected. Analysis of variance of the depth of disruption of the marked sediment indicated that different areas of the intertidal zone were disrupted to different depths. Caged marked sediment was disturbed to an average depth of 3.2 cm while unprotected sediment was disturbed to a mean depth of 11.1 cm. Deepest mixing occurred in a trough between sandwave crests and averaged 17.7 cm deep. These mixing depths are greater than the 1.2 cm deep disturbance produced by nonstorm wave action in the study area. 相似文献
15.
Spawning densities, spawning indices, egg densities, size distributions, and movement patterns of horseshoe crabs (Limulus polyphemus) were quantified for four coastal embayments (Monomoy National Wildlife Refuge, Pleasant Bay, Nauset Estuary, and Cape Cod Bay) on Cape Cod, Massachusetts from 2000 to 2002. Spawning activity was highest from mid May through mid June, but densities varied throughout the Cape Cod region. Average spawning densities (male and female crabs combined), measured using 25-m2 quadrats, were lower than 1 crab 25 m?2, although certain locations had consistently higher densities averaging 2 to 3 crabs 25 m?2 with individual survey densities recorded as high as 17 crabs 25 m?2. Spawning densities during night surveys were either similar or slightly higher than day surveys, except at a few sites within Pleasant Bay. Spawning indices were considerably lower ranging from 0 to 1.3 females 25 m?2 throughout the Cape Cod region. Spawning sex ratios varied from 1∶1.6 to 1∶3.1 (females:males) throughout the region, except within Pleasant Bay where highly male skewed ratios were observed (e.g., 1∶5.8, 3-yr average). Egg densities were low overall (<1 egg cm?2) throughout Cape Cod and egg densities tended to be higher in deeper sediments (5–20 cm deep) compared to shallow sediments (0–5 cm deep) at most locations. Over 7,800 horseshoe crabs were tagged on Cape Cod from 2000 to 2002. Average size and size frequency distributions of tagged crabs varied among regions. Larger individuals were observed at Monomoy National Wildlife Refuge while the smallest individuals were from Cape Cod Bay. We documented an overall recapture rate of 6.7% and our tag-recapture data indicated that 62% of crabs were recaptured at the original tagging location and 70% of recaptures traveled less than 2 km from the original tagging location, providing evidence for localized populations on Cape Cod. We have observed that horseshoe crabs differ among embayments within a regional area, suggesting the potential need for management plans specific to embayments or subregions depending on the characteristics of a population. 相似文献
16.
Populations of the American horseshoe crab (Limulus polyphemus) differ in broad areas of their biology. We observed a non-harvested, marked Florida Gulf coast population during their spring
spawning (March–May) in 11 years across a 17-year period (1992–2009). Long-term changes occurred in the number of spawning
pairs: the population was stable from 1992 to 2000 but increased markedly after 2000. Short-term variation in numbers of spawning
pairs, unpaired females, unpaired males, and operational sex ratios was explained by changes over the season and during each
week of spring tides and by differences in actual (not predicted) maximum high tide height. Wind direction strongly affected
tidal inundation and the number of spawning horseshoe crabs. Tagging individuals revealed that females returned to the nesting
beach less often than males and most females were re-sighted only within 1 week of spring tides. No animals were seen across
more than 6 years. Implications for management are discussed. 相似文献
17.
Knowledge of resource-use and movement patterns is a missing component in the development of horseshoe crab (Limulus polyphemus) management strategies. Available evidence indicates the potential for a variety of possible migratory behaviors, but the
lack of high-resolution, spatial-temporal data has hindered development of a year-round profile of ranging behavior. This
need was addressed in the present study by using acoustic telemetry to track the movements of adult horseshoe crabs in two
subembayments (Egypt and Hog Bays) of the Taunton Bay Estuary, Maine, from June 2003 to June 2005. Estimated mean total home
range sizes were 64.1 and 61.4 ha for breeding crabs tagged in Egypt and Hog Bays, respectively. We observed no horseshoe
crab dispersal to areas outside of the subembayments where they were tagged, so no mixing was observed between Egypt and Hog
Bay individuals despite a < 4-km separation. Observed shifts in movement patterns, resource use (subtidal versus intertidal),
and vagility facilitated a profile of seasonally partitioned horseshoe crab activity, which included late April to early May
post-wintering, June–July breeding, August–September pre-wintering, and October–April wintering, where space usage represented
about 10% of the mean total home range size. The apparent isolation of these resident populations implies a heightened vulnerability
to overexploitation and large-scale habitat alteration that might be more easily sustained by larger, more vagile populations.
This work underscores the need to apply horseshoe crab conservation, research, and management efforts at scales that are appropriate
to the ranging patterns of crabs, which first requires application of high-resolution methods to identify those patterns. 相似文献
18.
The Atlantic horsehoe crab,Limulus polyphemus, is harvested by the biomedical industry for Limulus Amoebocyte Lysate (LAL) a blood compound used to detect endotoxins,
for scientific research on vision, and as bait for the eel and conch fisheries. They are also subject to sources of natural
mortality such as consumption of eggs by shorebirds and stranding. Recently there has been growing concern over possible declines
inLimulus populations along the east coast of the United States. We have used stage-structured matrix modeling to improve our understanding
ofLimulus population dynamics in three Cape Cod estuaries (Stage Harbor, Pleasant Bay, and Barnstable Harbor) with differing harvest
pressures. The results suggest that a low level of harvest is sustainable, particularly if timing and size-specificity of
the harvest are taken into consideration. The model also suggests that efforts should be made to avoid harvesting crabs prior
to sexual maturity, as the population growth rate is more sensitive to changes in survival rate of older juveniles than of
other stages. The information the model provides could assist local and regional fisheries managers in establishing appropriate
regulations for the horseshoe crab fishery. 相似文献
19.
The American horseshoe crab, Limulus polyphemus, is found along the Atlantic and Gulf of Mexico coasts in genetically isolated populations. Eggs are laid in shoreline beaches that expose developing embryos to combinations of environmental stressors. Whether populations of L. polyphemus differ in multi-stressor tolerance had never been tested. We assessed the multi-stressor tolerance of L. polyphemus embryos from a population in Delaware Bay (DE) and determined whether these differed from the multi-stressor tolerance of embryos from a more southerly Florida Gulf Coast (FGC) population. We monitored the field sediment temperatures and determined multi-stressor tolerance of DE embryos, then compared these to published data for FGC embryos. For multi-stressor tolerance, we assessed development success of embryos in 2-week exposures to 36 full-factorial combinations of temperature (20, 25, 30, 35 °C), salinity (5, 15, and 34 ppt), and ambient O2 (5, 13, and 21% O2), followed by 2 weeks in recovery conditions. Sediment temperatures in the DE site ranged from 9.5 to 46 °C, with extended periods exceeding 35 °C. Development success was similar between the DE and FGC populations in 14 of 26 multi-stressor combinations. The DE embryos were generally more successful in conditions that included high temperature or moderate hyposalinity, whereas the FGC embryos were generally more successful in conditions that included extreme hyposalinity. This suggests that although multi-stressor tolerances are generally similar between the two populations, specific differences exist that correlate more with differences in nest microenvironment than latitude. 相似文献
20.
Chu-fa Tsai M. Nazrul Islam Rezaul Karim MD K. U. M. Shahidur Rahman 《Estuaries and Coasts》1981,4(2):127-138
Spawning biology and spawn fishery of three valuable species of Indian major carps,Catla catla, Labeo rohita andCirrhinus mrigala, in the lower Halda River, Bangladesh, were studied in 1978. The major carps spawned only in the Sonairchar oxbow-bend from April to June on or near the dates of the full moon and the new moon. The tide was then at its highest level, and there was heavy flood water runoff from the hill region with sharp increases in water level, turbidity and current velocity, as well as decreases in water temperature, dissolved oxygen, and hydrogen ion concentration. These three heterogeneric species, as a result of parallelism or convergence in evolution, overlap in their environmental requirements for spawning. The nursery ground of the major carp fry spawned in the Halda River was found to be in the Bay of Bengal. The brood stock origin is suspected to be at the Shankha River, 40 miles south of the Karnafuli River. The spawn fishery in the Halda River was intensive but inefficient. Engineering works and water management schemes are threatening the spawning habitat. 相似文献