Leistungsmessung an Bord von Fischereifahrzeugen zur Kontrolle der 300-PS-Begrenzung in der Schollenbox

For monitoring of the engine power of fishing vessels permitted for fishery in the plaice box with engine power of 300 HP or less at sea three different portable power measurement systems are developed and tested. A system measuring the twist of the propeller shaft by two divisible gearwheels mounted on the shaft worked well at shafts with roller bearing at both sides of the measured interval of 100–300 mm length. Only at a very few fishing vessels this system is applicable and therefore for monitoring purposes not suitable. The application of a commercial available system measuring the stress at the surface of the shaft was simplified for application by non experts. The torque is measured by strain gauges. The calibration of the system, measuring and recording of the power is done by a PC automatically. A small polished facet on the shaft protected against oxidation is needed for easy and quick application. In this case the system can be used by technical personnel of supervision boats for monitoring of the engine power at sea in a short time. A third power measurement system determinates the torque by measuring the displacement of two supports clamped on the shaft at a distance of 100 mm. The displacement is measured by a micrometer gauge mounted on one of the supports. Readout of the rotating gauge display is possible taking advantage of stroboscopic effect. The system needs no conditioning of the shaft and can be used by non technicians. The development is not finished until now and some additional investigations and tests are required. Additional measures for monitoring of the power on fishing vessels by self recording power measurement systems and sealed fuel racks with limited injection are reported and discussed.

Versuche mit einem modifizierten Rollengeschirr für Garnelenbaumkurren

With a traditional roller gear, only the rollers in the centre are working correctly. The rollers on both sides are more or less gliding on the sea bottom because their axis are not in a position perpendicular to the towing direction. Sediment is stirred up by these gliding rollers coupled with a negative bottom impact of this gear. With a modified roller gear for shrimp beam trawls the axis of all rollers are orientated 90° to the towing direction enabling all rollers to roll correctly on the sea bottom.

Long-term Trends in Catch Composition from Elasmobranch Derbies in Elkhorn Slough, California

Long-term trends in the elasmobranch assemblage of Elkhorn Slough, Monterey Bay, California, were analyzed by documenting species composition and catch per unit effort (CPUE) from 55 sport fishing derbies that occurred during May, June, and July, from 1951 until 1995. The most abundant species (bat ray, Myliobatis californica; shovelnose guitarfish, Rhinobatos productus; and leopard shark, Triakis semifasciata) were also analyzed for size-weight relationships, trends in size class distribution, stage of maturity, and sex ratios. Changes in species composition over the course of the derbies included the near complete disappearance of shovelnose guitarfish by the 1970’s and a slight increase in the abundance of minor species (mainly smoothhounds, Mustelus spp., and thornback, Platyrhinoidis triseriata) starting in the mid 1960’s. The relative abundance of bat rays in the catch steadily increased over the years while the relative abundance of leopard sharks declined during the last two decades. However the average number of bat rays and leopard sharks caught per derby declined during the last two decades. Fishing effort appeared to increase over the course of the derbies. There were no dramatic shifts in the size class distribution data for bat rays, leopard sharks, or shovelnose guitarfish. The catch of bat rays and leopard sharks was consistently dominated by immature individuals, while the catch of shovelnose guitarfish was heavily dominated by adults. There was evidence of sexual segregation in either immature or mature fish in all the species. Female bat rays and shovelnose guitarfish were larger than their male counterparts and outnumbered males nearly 2:1. Female and male leopard sharks were more nearly equal in size and sex ratio. Changes in species composition are likely due to fishing pressure, shifts in the prevailing oceanographic conditions, and habitat alteration in Elkhorn Slough. The sex ratios, stage of maturity, and size class distributions provide further evidence for the theory that Elkhorn Slough functions as a nursery habitat for bat rays and leopard sha