Answers to Hone Your Problem-Solving Skills Questions
1. Intensive fishing began at Catalina and San Nicolas Islands in the early 1980s. At Catalina Island, where fishing pressure continued from the
1980s through 2007, the size at which sheephead became sexually mature decreased from 213 mm in 1980 to 178 mm in 2007; the size at which sheephead changed sex decreased from 350 mm to 225 mm during the same time period.
At San Nicolas Island, fishing also appears to have affected size at maturation and size at sex change from 1980 to 1998, the time period during which intensive fishing occurred.2. We can answer this question using data at San Nicolas Island because the sheephead population at that location was subjected to intensive fishing from the 1980s through 1998, but then (starting in 1999) the population was protected from fishing. At that island, size at maturation and size at sex change declined from 1980 to 1998. However, by 2007 (8 years after protection from fishing began), both the size at maturation and the size at sex change had increased substantially—indicating that size at maturation and size at sex change can recover once fishing pressure is reduced.
3. Protection from fishing should have an immediate effect of increasing population abundance (since fewer fish are being killed by humans). In addition, protection from fishing causes the size at maturation and the size at sex change to increase in size. As a result, the size of fertile females will increase over time, causing the number of offspring produced per female to increase over time (since larger individuals are assumed to produce more offspring). This change in the number of offspring produced per female should cause population abundance to increase more rapidly than it otherwise would.