1 .		The most complete data on population levels of sandbar sharks, the most common shark in Chesapeake Bay, are from the long-term program of the VIMS Shark Ecology program. This program sampled 8 or more stations in and offshore of Chesapeake Bay from May through September or October annually over the period 1980 to present. Sharks were captured with 100-hook longlines stretched for 1 – 1.5 nautical miles (1.8 – 2.8 km) and fished 3 – 4 hoursi. Longlines are horizontally stretched ropes or heavy monofilament (the "mainline") with branches (the "gangions") containing hooks emanating from the mainline at fixed intervals. Although this method sounds dangerous, it generally does not harm the sharks (although some species fare more poorly than others), which are simply tagged and released. Commercial longlines, as you will later see, are a different matter. This typical longline set represents what fisheries scientists have termed one unit of effort. Data are reported as Catch Per Unit Effort (CPUE), that is, the number of sharks caught per 100 hooks per 3 – 4 hour fishing time. Consider the following data in Table 1: Table 1. Mean CPUE (sharks per hundred hooks per 3–4 hour set, estimated from a graph and thus not necessarily exact) for adult C. plumbeus Year CPUE 1980 0.98 1981 0.83 1990 0.14 1991 0.08 1992 0.03 1993 0.17 1994 No Data Available 1995 0.07 1996 0.12 1997 0.06 1998 0.04 Plot these data on a separate sheet using a bar graph. Label the x-axis "Year" and the y-axis "CPUE."   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
2 .		Interpret the graph. What trends can you infer?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
3 .		List as many possible explanations as you can for the decline in the sandbar shark population. Refer back to your textbook, if necessary.   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
4 .		Sandbar sharks are second only to blue sharks in popularity with recreational fishers. Moreover, because there is a lucrative overseas market for shark fins and the sandbar shark’s fins are so large, they are even more valuable. Shark fins are used in Chinese shark fin soup. Depending on the species from which the fins were obtained, retail prices for shark fins range from $40 – 564 U.S. dollars per kilogram. Finally, sandbar sharks are a popular food fish along the East Coast. Visit this site containing shark recipes. In this particular case, the explanation for the population decrease in sandbar sharks could be overfishing. Sharks have become very popular as an upscale food fish in the last 20 years. Suggest explanations for this.(Hint)   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
5 .		Let’s examine some more data (Table 2): Table 2. Commercial Sandbar Shark Landings in Chesapeake Bay (from the VIMS Annual Progress Report, 1998-99) Year Landings (pounds) 1993 4,000 1994 1,500 1995 20,000 1996 43,000 1997 20,500 From 1993 to 1997, interpret the overall trend in sandbar shark landings.   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
6 .		From 1996 to 1997, you have already seen from Tables 1 and 2 that both the CPUE and commercial shark landings dropped. Can you conclude with absolute certainty that overfishing caused the decline? Does it seem likely that overfishing could have played a role?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
7 .		Because catch rates are an indicator of population size, your analysis of CPUE data for sandbar sharks likely concluded that adult stocks are severely depleted. Let’s now examine juvenile sandbar shark capture rates. Table 3. Mean CPUE (sharks per hundred hooks per 3–4 hour set) for juvenile C. plumbeus) Year CPUE 1980 1.3 1981 0.52 1990 0.17 1991 0.03 1992 0.28 1993 0.22 1994 No Data Available 1995 0.62 1996 1.03 1997 1.45 1998 2.25 Plot these data on a separate sheet, and then answer the next question after reading the short paragraph. Juvenile populations may be showing some recovery from an earlier depletion or may simply be increasing due to a variety of possible factors. According to experts. the apparent recovery of populations of juveniles is most likely because their chief predators, large sharks (including adult C. plumbeus), are disappearing. Recovery of this species will not occur until fishing pressure on all sizes of sandbar sharks is reduced. Describe trends in the graph. What conclusion can you draw about the health of juvenile sandbar shark populations?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
8 .		Now, let’s examine the population growth rates for sandbar sharks. According to researchers, under conditions of "natural mortality" the sandbar shark population would grow at between 6.4 and 12% per year. Natural mortality is about 10% per year and excludes losses from fishing. Using the doubling time formual(70/R) and the 6.4% rate of population growth, project when sandbar shark populations would reach twice their present level. Theoretically, when would the population reach 1000 times its current level?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
9 .		For a population growing exponentially, it takes 10 doubling times to grow to 1024 times its current level. In practice, we round 1024 to 1000. Thus, for this population growing at 6.4% to grow 1000-fold would take 10 doubling periods (10 x 10.9 years), or 109 years. If you’re wondering why the oceans are not overrun with sharks, it is because population increases of one thousandfold are not likely to occur in apex predators such as sharks. Mortality in sharks and many other organisms (e.g. dolphins, lions, wolves, elk) is said to be "density-dependent," meaning that there is a compensatory increase in mortality (increased predation on sharks, increased incidence of disease; decreased survival among neonates [newborns], decreased success as predators) as population size increases. This serves to maintain populations at or near the environment’s "carrying capacity." In actuality, true mortality is not 10% per year as we assumed, but closer to 35% because of harvesting by fishers. Under these conditions, sandbar shark populations would decrease at a rate of 7% per year because sharks are dying before reproducing and in greater numbers than are born each year. Using the halving time formula (70/k) and the 7% rate of population decrease, calculate when sandbar shark populations would reach half their present level.   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
10 .		Although many life history characteristics of sharks make them vulnerable to overfishing and other threats, there is one advantage in having few offspring and a long gestation period. What do you think this advantage might be? (Hint)   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.