Fisheries that target fish spawning aggregations can exhibit hyperstability, in which catch per unit effort (CPUE) remains elevated as stock abundance declines, but empirical support is limited. We ...compiled several fishery-dependent and fishery-independent data sets to assess stock trends in the barred sand bass (
Paralabrax nebulifer
) and the kelp bass (
Paralabrax clathratus
) in southern California, USA, evaluate the interaction between spawning aggregations and fishing activities, and test for hyperstability. Annual and seasonal trends from fisheries and population data indicate that regional stocks of both species have collapsed in response to overfishing of spawning aggregations and changes in environmental conditions. The aggregating behavior of fish and persistent targeting of spawning aggregations by recreational fisheries combined to produce a hyperstable relationship between CPUE and stock abundance in both species, which created the illusion that population levels were stable and masked fishery collapses. Differences in the rate of decline between the two species may be related to the size, duration, and spatial distribution of their spawning aggregations. Results of this study provide empirical evidence of hyperstability in aggregation-based fisheries and demonstrate that CPUE data be used with caution and given low weight when fishery-independent data are available.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Co‐operation in the management of shared fish stocks is often necessary to achieve sustainability and reduce uncertainty. The United States of America (USA) and Mexico share a number of fish stocks ...and marine ecosystems, while there is some binational co‐operation in scientific research, unilateral management decisions are generally the rule. We present a case study using the giant sea bass (Stereolepis gigas, Polyprionidae) to highlight how these management and research asymmetries can skew national perceptions of population status for a fully transboundary species. Scientific publications and annual funding related to giant sea bass are 7x and 25x higher in the USA, respectively, despite the fact that 73% of the species’ range occurs in Mexico. Conversely, annual fishery production and consumptive value of giant sea bass in Mexico are 19x and 3.5x higher than in the USA, respectively, while the non‐consumptive value related to dive ecotourism is 76x higher in the USA. These asymmetries have generated a distorted view of the population status of the giant sea bass across its entire range. This and other factors related to historical fishery dynamics and policy must be accounted for when assessing population status, and subsequent appropriate management responses, across geopolitical boundaries.
Recent study suggest the globally distributed yellowtail amberjack, Seriola lalandi sensu lato, is a complex of three closely related species. Together, these and three other species of Seriola ...comprise an important component of global aquaculture production with an estimated annual value of $1.3 billion. As yellowtail aquaculture grows, the impact of unintentional releases on wild populations has become an increasingly important issue, particularly in light of international trade of hatchery seed. To create a genetic baseline, we examined spatial genetic structure in 260 specimens collected from seven locations over a wide geographical range using 15 nuclear microsatellites and mitochondrial control region sequences. Overall genetic differentiation among locations, as revealed by microsatellite data, was highly significant (FST = 0.085, DEST = 0.382, P < 0.001), and pairwise estimates of divergence derived from mitochondrial and microsatellite data support the presence of four significantly differentiated populations corresponding to the N.E. Pacific, N.W. Pacific, S. Pacific, and South Atlantic. Based on the genetic differentiation detected in this study, and recently published sequence data, these populations more accurately reflect the presence of at least three cryptic species of Seriola. Especially strong genetic differentiation between hemispheres indicates that the equatorial region is a significant dispersal barrier for yellowtail. This study represents the broadest geographic investigation of genetic population structure conducted, to date, for specimens of the S. lalandi complex.
What to do about fisheries collapse and the decline of large fishes in marine ecosystems is a critical debate on a global scale. To address one aspect of this debate, a major fisheries management ...action, the removal of gill nets in 1994 from the nearshore arena in the Southern California Bight (34°26′30″N, 120°27′09″W to 33°32′03″N, 117°07′28″W) was analyzed. First, the impetus for the gill net ban was the crash of the commercial fishery for white seabass (
Atractoscion nobilis
; Sciaenidae) in the early 1980s. From 1982 to 1997 catch remained at a historically low level (47.8 ± 3.0 mt) when compared to landings from 1936–1981, but increased significantly from 1995–2004 (
r
= 0.89,
P
< 0.01) to within the 95% confidence limit of the historic California landings. After the white seabass fishery crashed in the early 1980s, landings of soupfin (
Galeorhinus galeus
; Triakidae) and leopard shark (
Triakis semifasciata
; Triakidae) also significantly declined (
r
= 0.95,
P
< 0.01 and
r
= 0.91,
P
< 0.01, respectively) until the gill net closure. After the closure both soupfin and leopard shark significantly increased in CPUE (
r
= 0.72,
P
= 0.02 and
r
= 0.87,
P
< 0.01, respectively). Finally, giant sea bass (
Stereolepis gigas
; Polyprionidae) the apex predatory fish in this ecosystem, which was protected from commercial and recreational fishing in 1981, were not observed in a quarterly scientific SCUBA monitoring program from 1974 to 2001 but reappeared in 2002–2004. In addition, CPUE of giant seabass increased significantly from 1995 to 2004 (
r
= 0.82,
P
< 0.01) in the gill net monitoring program. The trends in abundance of these fishes return were not correlated with sea surface temperature (SST), the Pacific Decadal Oscillation (PDO) or the El Niño/Southern Oscillation (ENSO). All four species increased significantly in either commercial catch, CPUE, or in the SCUBA monitoring program after the 1994 gill net closure, whereas they had declined significantly, crashed, or were absent prior to this action. This suggests that removing gill nets from coastal ecosystems has a positive impact on large marine fishes.
•A single population of giant sea bass exists between southern California and the Pacific side of Baja California, Mexico.•Mitochondrial and nuclear genetic diversity is low for this population.•As a ...result of reduced genetic diversity, the contemporary effective population size of this population is less than 500 individuals indicating that an immediate change in the management of fisheries targeting the species is needed.
The giant sea bass, Stereolepis gigas (Polyprionidae), is the largest teleost distributed in the northeastern Pacific from California to northern Mexico and has been overexploited by fisheries for more than a century. As a consequence of this historic exploitation, populations collapsed throughout the region in the last century resulting in the listing of the species as Critically Endangered by the IUCN. Recently, numbers of giant sea bass have been increasing within the region due primarily to the banning of the near shore gill net fishery in California waters in 1994. To assess population structure, the impact of historic exploitation on the genetic diversity and effective population size of the species, and to detect signs of recent population expansions, individuals from throughout the northeastern Pacific (n=61; Northern Channel Islands, CA to San Quintín, Baja California) were sequenced at the mitochondrial control region and genotyped using 12 nuclear microsatellite loci generated from next-generation sequencing. Based on these markers, a single population was detected with low genetic diversity resulting in an estimated contemporary effective population size of less than 500 individuals with evidence of recent expansion within the region.
For fishes that migrate to specific locations to spawn within large aggregations at predictable times, fishery independent surveys of the abundance, distribution, and population structure of adult ...fish at spawning aggregation sites can provide valuable data for fisheries monitoring and assessments. We tested the feasibility of using high resolution, split-beam sonar to estimate the distribution, abundance, and group sizes of Barred Sand Bass (Paralabrax nebulifer) at their primary spawning aggregation site off Huntington Beach, California, in July 2010 and July 2012. We established an in-situ target strength distribution for Barred Sand Bass using tethered fish, collected hydroacoustic data opportunistically over the entire spawning grounds, and validated acoustic data with concurrent video surveys and rod and reel sampling of fishes present within the survey area. The modal target strength of Barred Sand Bass was determined to be -35 dB and was distinct from other fish species present. Groups of Barred Sand Bass averaged 30 individuals in abundance and ranged from 2 to 1,711 individuals, with the vast majority of the groups containing less than 10 individuals. Groups of Barred Sand Bass were most abundant in the water column between 5 and 10 m below the surface over bottoms depths of 20 to 30 m, resulting in a negative relationship between group size and depth. Due to the sand bottom habitat of the spawning site, the tendency for fish to aggregate to spawn in the water column during predictable periods, and the low diversity of other fish species present at the spawning site during the peak spawning months, hydroacoustic surveys of primary spawning aggregation sites represent an efficient, practical method for regional population monitoring and fishery assessments of Barred Sand Bass.
Nearshore, coastal and embayment areas off southern California were sampled to determine the spatial and temporal patterns abundance and size distributions of young white seabass in the shallow (5–14
...m) waters from Santa Barbara south to Imperial Beach off San Diego. A total of 19 stations, 13 in nearshore coastal waters and 6 in embayments, dispersed along the Southern California Bight were surveyed in each sampling month using 45.7
m variable mesh, monofilament gill nets. In the 11-year period of sampling (April 1995–June 2005), a total of 8075 juvenile white seabass was captured in 42 sampling months. The mean catch-per-unit-effort (CPUE: 2.0
fish/net
±
0.2) for juvenile white seabass varied significantly among stations during the 10-year period (1996–2005) of the full station sampling. Stations located near large rocky headlands, such as Palos Verdes, Santa Barbara, Newport, and La Jolla yielded the highest catches. Although CPUE peaked in August 1999 as a result of strong year classes in 1996–1998, overall, catches tripled over the 11-year sampling period at seven coastal sites increasing significantly at a rate equivalent to 0.22
fish/(net
year). These relatively high catches of wild, juvenile fish over the last decade, along with significant increases in commercial CPUE and increased recreational catches overall, indicate that the natural population of white seabass is in the process of recovery. Commercial catches are again comparable to levels attained prior to the fishery collapse in the 1970s and 1980s. Therefore, we propose that the white seabass now represents one of the first documented cases of a recovering, demersal species of commercial importance. The ban of nearshore commercial gill net fishing by Proposition 132 probably contributed greatly to the increase in the population size that led to this recovery. In addition, the succession of warm water years that occurred from 1983 to the strong El Niño event of 1997–1998 also played an important role in the successful recruitment of white seabass.
