Wilk et al. (1977) reported data on the number and types of fishes and environmental data for the area of the Atlantic continental shelf between eastern Long Island, New York and Cape May, New Jersey. The ocean survey area was divided into strata based on depth. Sampling was done at a higher rate close to shore than farther away from shore: “In-shore strata (0–28 m) were sampled at a rate of approximately one station per 515 km2 and off-shore strata (29–366 m) were sampled at a rate of approximately one station per 1,030 km2” (p. 1). Thus each record in strata 3–6 represents twice as much area as each record in strata 1 and 2. In calculating average numbers of fish caught and numbers of species, we may use a relative sampling weight of 1 for strata 1 and 2, and weight 2 for strata 3–6.

The data file nybight.dat contains data on the total catch for sampling stations visited in June 1974 and June 1975.
a. Construct side-by-side boxplots of the number of fish caught in the trawls in June, 1974. Does there appear to be a large variation among the strata?
b. Calculate estimates of the average number and average weight of fish caught per haul in June 1974, along with the standard error.
c. Calculate estimates of the average number and average weight of fish caught per haul in June 1975, along with the standard error.
d. Is there evidence that the average weight of fish caught per haul differ between
June 1974 and June 1975? Answer using an appropriate hypothesis test.