Does the California market squid (Loligo opalescens) spawn naturally during the day or at night? A note on the successful use of ROVs to obtain basic fisheries biology data

The California market squid (Loligo opalescens Berry), also known as the opalescent inshore squid (FAO), plays a central role in the nearshore ecological communities of the west coast of the United States (Morejohn et al., 1978; Hixon, 1983) and it is also a prime focus of California fisheries, ranking first in dollar value and tons landed in recent years (Vojkovich, 1998). The life span of this species is only 7−10 months after hatching, as ascertained by aging statoliths (Butler et al., 1999; Jackson, 1994; Jackson and Domier, 2003) and mariculture trials (Yang, et al., 1986). Thus, annual recruitment is required to sustain the population. The spawning season ranges from April to November and spawning peaks from May to June. In some years there can be a smaller second peak in November. In Monterey Bay, the squids are fished directly on the egg beds, and the consequences of this practice for conservation and fisheries management are unknown but of some concern (Hanlon, 1998). Beginning in April 2000, we began a study of the in situ spawning behavior of L. opalescens in the southern Monterey Bay fishing area.

Yield- and biomass-per-recruit analysis for rotational fisheries, with an application to the Atlantic sea scallop (Placopecten magellanicus)

A general model for yield-per-recruit analysis of rotational (periodic) fisheries is developed and applied to the sea scallop (Placopecten magellanicus) fishery of the northwest Atlantic. Rotational fishing slightly increases both yield- and biomass-per-recruit for sea scallops at FMAX. These quantities decline less quickly when fishing mortality is increased beyond FMAX than when fishing is at a constant rate. The improvement in biomass-per-recruit appears to be nearly independent of the selectivity pattern but increased size-at-entry can reduce or eliminate the yield-per-recruit advantage of rotation. Area closures and rotational fishing can cause difficulties with the use of standard spatially averaged fishing mortality metrics and reference points. The concept of temporally averaged fishing mortality is introduced as one that is more appropriate for sedentary resources when fishing mortality varies in time and space.

Zooplankton biomass along the west coast of India and its effect on the fishery

The coastal zone along the west coast of India is very productive with a mean secondary production rate of 5.89 mg C/m super(3)/day. Statewise, maximum zooplankton standing stock was observed off Maharashtra. The existing yield of fishery from the surveyed region has been compared with the estimated sustainable fishery potential.

Mortality rates of the Poovalan prawn (Metapenaeus dobsoni) along the southwest coast of India with a note on the dynamics of its population

The annual instantaneous total mortality coefficient (Z) for the prawn Metapenaeus dobsoni has been estimated to range from 0.8 to 5.14 by the cumulative catch curve method. Different methods used in the study resulted in wide ranging values of natural mortality (M) (0.6 to 2.303), but the yield per recruit model when superimposed with the absolute yield values revealed the right order to be > 2. The biologically optimum yield of about 18 thousand tons is obtained for an effort of 2,702 trawlers per day for 215 fishing days when the annual exploitation ratio (E) is about 52%.

Estimation of maximum sustainable yield (MSY) of hilsa (Tenualosa ilisha Ham.) in the Meghna river of Bangladesh

MSY per recruit of Tenualosa ilisha in the Meghna river was predicted as 112 g per recruit at the F(msy)=0.6/yr and at T(c)=0.6/yr. But Y/R=95 g per recruit was obtained at the existing fishing level, F=1.14/yr and at T(c)=0.6/yr. Existing F level was nearly double than the F(msy) level. Fishing pressure should be reduced immediately from F=1.14/yr to F(msy)=0.6/yr. F(msy)=1.14/yr was the same at first capture, T(c)=1.0, 1.2 and 1.4/yr, and MSY could be obtained as 142 g, 162 g and 176 g per recruit respectively. It is easier to change the first capture age (Tc) rather than changing off level. So, hilsa fishery manager may adopt F(msy)=1.14/yr while age at first capture must be increased from T(c)=0.6/yr (3 cm size group) to T(c)=1.4/yr (25 cm size group), by which 1.8 times production could be increased than the present production. MSY also possible to obtain as 201 g and 210 g per recruit at F(msy)=2.0/yr and 4.0/yr at T(c)=1.7/yr and 1.9/yr respectively. Under both the situations, hilsa production could be increased 2 times than the present production. To obtain the MSY=210 g per recruit the fishing level could be increased up to F=4.0/yr at T(c)=1.9/yr (34 cm size group). Economic point of view, hilsa fishery managers may choose to obtain the economic MSY as 201 g per recruit at F(msy)=2.0/yr and T(c)=1.7yr (31 cm size group) in the Meghna river of Bangladesh.

Stock assessment and biology of Johnius glaucus (Day) off the northwest coast of India

The stock size and biology of Johnius glaucus (Day) resource off the northwest coast of India were studied for 1982-83 and 1983-84. The total length at the end of 6, 12, 18, 24 and 26 months was 121 mm, 183 mm, 237 mm, 261 mm and 264 mm respectively. The length growth parameters were: L∞=300 mm, K=0.0807 (monthly) and t(sub)0=-0.51 month. The weight growth parameters were: W∞= 317g, K=0.0762 (monthly) and t(sub)0= -0.41 month. The exploited stock mainly composed of 1/2 + and 1+ age groups. The annual Z, M and F were 2.34, 1.49 and 0.85 respectively. The l(sub)b, t(sub)b, l(sub)r, t(sub)r and selection factor K were 155 mm, 0.75 year, 65 mm, 0.25 year and 3.875 respectively. The Yw/R was optimum at the exploitation rate (E) of 0.75 and coded mesh size of 37 mm. The total stock for 1982-83 and 1983-84 was 14,624 and 26,190 tons respectively. The standing stock of 1982-83 and 1983-84 was 5,645 and 10,110 tons respectively. The MSY for 1982-83 and 1983-84 was 6,623 and 11,788 tons respectively. The F and Z were lowest in 0+ age group and highest in 1+ age group.