Bottom Trawl Surveys - Proceedings of a Workshop Held at Ottawa ...

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herring were set in comparable depths on both sides of the channnel and left in position overnight. Results are not sufficient for analysis but it is worth noting that more shrimp were caught in the unfishable grounds (45 vs. 7). These untrawlable areas are not included in the estimates of biomass and it is not known to what degree shrimp in these areas contribute to the fishable stock. Therefore, biomass is further underestimated to some extent. CONCLUSIONS Research surveys to estimate shrimp abundance are questionable in terms of their usefulness. In areas such as the Gulf of St. Lawrence, it appears that reasonable estimates of stock size can be obtained from surveys conducted during daylight hours. In areas such as Labrador and the Davis Strait variation associated with the data used to extrapolate biomass is unacceptable. Bottom photography used in the latter area also involves extreme variability. Attempts to solve the problem, or at least reduce it to acceptable levels, have met with limited success. Increased sample size in areas off Labrador has resulted in some improvement but indicates as well that high sampling density is necessary in relatively small areas, and in larger areas such coverage cannot possibly be achieved. Accounting for the pattern of diel vert i ca 1 migration pr.esents addition a 1 problems. The desired effects are not always attained. It also appears that the patterns themselves are variable perhaps on a daily basis and influencing factors such as light intensity, currents, fishing pressure, season, depth, gear and area cannot be ruled out. The question of stratified random versus line surveys is academic considering the state of the art, and, since some of the areas being studied are not well defined topographically, the line surveys becomes more attractive if only for convenience. Mean biomass estimates from two surveys in the Davis Strait in 1979 were similar; one used the line method and the other the stratified random method (Parsons 1979; Dupouy et al. 1979). Alternatives are challenging. Acoustic methods may have potential but will require considerable research to interpret data which are masked in bottom echos or echos from associated fish species. Underwater photography may be of some assistance in solving these problems. Abundance-meteorological relationships should be given high priority (Dow 1979), not necessarily to replace the trawl survey but perhaps to refine data which they produce. Association with other species which are more "well-behaved" provides another possible alternative. The patterns of feeding by a major shrimp predator such as Greenland halibut may give some insight into relative shrimp abundance. While new ideas are investigated and the commercial data base increases, it appears that the surveys must continue. There are a number of suggestions which can be forwarded to ameliorate the accumulating data. Horizontal openings of various gears used can and must be measured with considerable accuracy. Settling and retrieval times for gear under different circumstances should be monitored and used in conjunction with accurate records of distance covered by the net to determine area swept during each set. Sample size should be 145 maximized and data on vertical migrations should be collected with each survey. (Depending on the area it may be more appropriate to increase sample size than spend considerable time monitoring diel effects.) Some idea of the seasonal distribution is mandatory so that surveys can be timed to coincide with periods of maximum density. Areas which appear unfishable must be considered in relation to potential shrimp distribution and, more importantly, their contribution (if any) to the fishable stock. And, finally, attention must be paid to understand the effects of winds and currents in affecting the speed of tow and behaviour of the gear, behaviour of the shrimps, or both. REFERENCES Anonymous. 1978a. Report on literature review of pink shrimp fishery potential in northeastern Canadian waters for Supply and Services Canada and Fisheries and Environment Canada. Maclaren Marex, Inc. Anonymous. 1978b. Report on exploratory fishing assessment of pink shrimp fishery potential in northeastern Canadian waters for Supply and Services Canada and Fisheries and Environment Canada. Maclaren Marex, Inc. Balsiger, J.W. 1979. A review of pandalid shrimp fisheries in the Northern Hemisphere. Pandalid Shrimp Workshop, Kodiak, Alaska, Feb. 13-15, 1979. · Carlsson, D.M. 1979. Review and discussion of current stock assessment techniques used in the management of Greenland shrimp resources. Pandalid Shrimp Workshop, Kodiak, Alaska, Feb. 13-15, 1979. Carlsson, D.M., Sv. Aa. Horsted and P. Kanneworff. 1978. Danish trawl surveys on the offshore West Greenland shrimp grounds in 1977 and previous years. ICNAF Sel. Papers 4: 67-74. Dow, R.L. 1979. Management strategy for Pandalus borealis in the Gulf of Maine. Pandal1d Shr1mp Workshop, Kodiak, Alaska, Feb. 13-15, 1979.
146 Dupouy, H., J. Frechette and C. Leroy. MS 1979. Biomass estimates of the northern deepwater shrimp, Pandalus borealis, in NAFO Divisions 1B and OB - R/V Thelassa survey, September-October 1979. NAFO SCR Doc. 79/XI/6, Ser. No. N017. Frechette, J. 1979. Shrimp fishery Pandalus borealis in Quebec. Pandalid Shrimp Workshop, Kodiak, Alaska, Feb. 13-15, 1979. Grosslein, M.D. 1971. Some observations on the accuracy of abundance indices derived from Research Vessel Surveys. ICNAF Redbook 1971, Part 111: 249-266. Haynes, E.B. and R.L. Wigley. 1969. Biology of the Northern shrimp, Pandalus borealis, in the Gulf of Maine. Trans. Am. Fish. Soc. 98(1): 60-76. Kanneworff, P. MS 1979. Stock biomass 1979 of shrimp (Pandalus borealis) in NAFO Subarea 1 estimated by means of bottom photography. NAFO SCR Doc. 79/XI/9, Ser. No. N020. Parsons, D.G. MS 1978. Effects of a by-catch of young redfish in the Port au Choix shrimp fishery- First implications. CAFSAC Res. Doc. 78/8. ------ MS 1979. Canadian research efforts for shrimp (Pandalus borealis) in Division OA and Subarea 1 1n 1979. NAFO SCR Doc. 79/XI/7, Ser. No. N018. Parsons, D.G., G.E. Tucker and P.J. Veitch. MS 1979. An assessment of the Labrador shrimp fishery. CAFSAC Res. Doc. 79/1. ------ MS 1980. Status of the Labrador pink shrimp resources, Divisions 2H and 2J. CAFSAC Res. Doc. 80/14. Sandeman, E.J. MS 1978a. Shrimp (Pandalus borealis) in the Labrador area- A first assessment. CAFSAC Res. Doc. 78/1. MS 1978b. An assessment of the stock of shrimp (Pandalus borealis) in the Esquiman Channel, Gulf of St. Lawrence. CAFSAC Res. Doc. 78/26. Smidt, E. 1978. Diurnal variation in shrimp catches on the offshore grounds in ICNAF Divisions 1B and 1C. ICNAF Sel. Papers 4: 45-46. Squires, H.J. 1967. Relation of temperature to growth and self-propagation of Pandalus borealis in Newfoundland. Report on FAO World Sc1entific Conference on the Biology and Culture of Shrimps and Prawns, 1967. Ulltang, 0. 1979. The Norwegian shrimp fisheries - History of research and management. Pandalid Shrimp Workshop, Kodiak, Alaska, Feb. 13-15, 1979. Warren, J.S. 1976. The morphology of two transverse channels on the northeast Newfoundland shelf. Maritime Sediments 12(1): 19-32.
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Canadian Special Publication of Fis
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iv TABLE OF CONTENTS/TABLE DES MATI
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Abstract Doubleday; W.G., and D. Ri
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4 Research vessel operating expendi
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6) That sensitivity analyses relati
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List of Participants/Liste des Part
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Division 30 Division 3N Table l. co
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45"00 Yi Fig. 12. Contour diagram o
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66 When departing on a survey, each
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68 ABUNDANCE ESTIMATES OF THE TRAWL
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-:... "' "' 3 _..-bob in 0 35cm Fig
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74 wires length (m) 1250 1000 7 50
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78 200 150 100 50 • • • •
Page 94: CATCH PROJECTIONS AND THEIR RELATIO
Page 102: AGE 3 4 5 6 7 8 9 10 11 12 13 14 15
Page 106: TABLE B. Relative error (expressed
Page 110 and 111: contribute significantly to the est
Page 113: 114 It is seldom the case that surv
Page 123 and 124: 124 GROUNDFISH SURVEY TECHNIQUES AS
Page 125 and 126: 126 The area bounded by the 100-fat
Page 131: 132 Table 2. Biomass estimates, Esq
Page 135: 136 Table 6. Esquiman Channel, Gulf
Page 139: 140 Table 10. Shrimp biomass estima
Page 147: ABUNDANCE ESTIMATORS BASED ON STRAT
Page 167 and 168: to be exact. Monte Carlo simulation
Page 173: EXAHPLE 2 Haddock in NAFO Division
Page 176 and 177: 178 ANALYSIS OF VARIANCE SOURCE CON
Page 179: SUMMER DISTRIBUTION OF GROUNDFISHES
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194 DISTRIBUTION AND SAMPLING VARIA
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Fig. 4 ' cont'd 205
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66' 62' 46' COD 1976 62' 1978 60' 6
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46" u• 46" 66" 64" 62" 64" 62" oo
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216 arhythmic in spring-early summe
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226 Tableau 5 - Pourcentage cumulat
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230 Much further work on fish swimm
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Table 3b. Variation of s (feet/sec
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250 FISH BEHAVIOUR IS A MAJOR FACTO
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professional fisherman. No matter h
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270 10 8 6 4 2 8 6 4 2 10 8 6 4 2 1
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