Relative Abundance and Distribution 

 of Major Species 



Since Jainuary 1963, we have assessed the 

 relative abundance in the Galveston estuary of 

 the species most frequently caught in a small 

 trawl. Of the more than 150 species offish, 

 crab, and shrimp collected, 9 estuary- 

 dependent species made-up more than 80 per- 

 cent of all animals caught for each of the past 

 3 years. These species are: Atlaintic croaker, 

 Micropogon undulatus ; bay ainchovy, Anchoa 

 mitchilli ; brown shrimp; white shrimp; spot, 

 Leiostomus xanthurus ; sand seat rout, Cynos- 

 cion arenarius ; blue crab, Callinectes sapidus ; 

 sea catfish, Galeichthys felis ; and large- 

 scale menhaden, Brevoortia patronus . All but 

 the bay anchovy, an abundsint forage fish, are 

 of direct commercial importance. 



Annual variation in the relative abundance 

 of these nine species is considerable. The 

 abundance of croaker, anchovy, menhaden, 

 sand seatrout, sea catfish, and brown amd 

 white shrimp was higher in 1965 than in 1963 

 or 1964. Thus, 1965 was well above average 

 for many species. Interspecific competition 

 and predation were probably not major con- 

 trolling factors. Abundcince of these same 

 species was generally lowest in 1964. Only 

 the blue crab and spot reached their maximum 

 abundance in 1964. 



These species demonstrated a preference 

 for a particular part of the estuary. East Bay 

 harbored greater numbers of croaker, sand 

 seatrout, spot, and white and brown shrimp 

 than any other subbay. Menhaden, sea catfish, 

 and blue crabs were most numerous in upper 

 Galveston Bay, whereas bay anchovies were 

 most abundant in Trinity Bay. 



Each species alsodennonstratedapreference 

 for a specific type of habitat in the subbays. 

 Considerably more menhaden, spot, croaker, 

 blue crabs, and white amd brown shrimp were 

 caught in the peripheral waters of the estuary 

 than elsewhere. Only the bay cinchovy demon- 

 strated a preference for the open-bay waters 

 and the sea catfish for the near-shore waters. 

 The sand seatrout was equally abundant in the 

 open and peripheral waters. 



In view of the rapid deterioration of our 

 estuarine habitat, every effort should be made 

 to conserve the natural environment of East 

 Bay and its bordering peripheral areas. 



Brown Shrimp Study 



The brown shrimp is the moat valuable 

 species taken commercially from Texas 

 coastal waters. We have san-ipled the juvenile 

 population in Galveston Bay since 1963 to 

 estimate their relative abundance aind possibly 

 provide a rough index of the annount of shrimp 

 that might be available to the fishery (fig. 24). 

 The year 1963 was relatively good for brown 

 shrimp in Texas; 1964 was poorer; and 1965 



ISO 

 100 - 



50 



- 



-I 



I 400j; 



a 250 



UJ 



^ 200 



<2 150 



(/) 



UJ 100 



5 



50 



Jl 



1966 



iJ 



S 

 in 

 cr 



UJ 

 Q. 



I 

 < 



I96S 







150 



100 



50 







I50|- 



100 - 



50 







LlLJ 



L 



(964 



L_ 



11963 I 

 I ■ - I 



APR. MAY JUN. JUL. AUG 'AVERAGE 



APR-JUN. 



Figure 24. — Relative abundance of Juvenile brown shrimp 

 In the Galveston estuary. 



was the best of the three. If we relied on 

 numbers alone, however, 1965 should have 

 set an alltime record for harvest because 

 fantastic numbers of juvenile brown shrimp 

 were present in the estuary. The 1966 crop of 

 brown shrimp in Galveston Bay is probably 

 greater them in 1964 but less than in 1963 or 

 1965. 



This abundance index is at best only relative 

 between years, and its interpretation is com- 

 plicated by many factors. The time of the year 

 when the juvenile population in the bay reaches 

 peak abundance (as indicated by trawl sampling 

 where only shrimp larger than 40 mm. are 

 retained) varies between years. Furthermore, 

 shrimp frequently leave the estuary at a dif- 

 ferent average size and at different times from 

 year to year. 



MaLximum abundamce of juvenile brown 

 shrimp occurred in May 1963, 1964, and 1965, 

 but in early June in 1966. A cool, late spring 

 in 1966 may have retarded growth sufficiently 

 so that they were not big enough to be cap- 

 tured in our trawls until later in the season. 



The period of heavy emigration of brown 

 shrimp from the estuary cam start as early 

 as mid-May or as late as early June. In 1963 

 and 1964, emigration was not significant until 

 early June, whereas in 1965 large numbers of 

 shrimp left the estuary in mid-May amd 



24 



