4.4 Biological Resources
The effects of suspended particulates on plankton are generally considered to be negligible because of the
limited area affected and short exposure time as they drift through the affected area. Fish offshore the
receiver sites, and any marine mammals that ventured close to shore, may temporarily leave the area
affected by turbidity, but would not be expected to be adversely affected in the long-term. Some studies
of beach replenishment have observed fish attraction to turbidity plumes, presumably to feed upon dead
invertebrates and organic particulates that are washed offshore.
Fish-eating birds such as the California brown pelican and California least tern could be impacted in the
vicinity of the receiver site by a temporary reduction in their prey base if fish move away from the turbidity
plume. Given that turbidity would be localized and not extend from site to site, turbidity would not extend
beyond normal foraging distances for either of these species. California least tern forage generally within
a two-mile radius of their nesting site, but may forage as far as five miles away. California brown pelicans
forage over several miles. Since ample alternative forage areas would be available to these species during
receiver site construction, particularly during non-nesting periods, no adverse impacts to these species are
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anticipated. There may even be a temporary attraction to the plume areas if fish concentrate within the
plume. Monitoring of a beach replenishment project in Orange County demonstrated that California least
tern preferred to forage inside the turbidity plume (MEC 1997). Attraction of fish-eating birds to dredge
areas has also been noted in San Diego Bay.
With the project schedule shifted from later summer to the spring nesting season (April to September),
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additional analysis was undertaken to evaluate potential turbidity impacts to least tern foraging. The least
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tern can forage up to five miles distant, but prefers to remain closer (two miles or less) during the nesting
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season when eggs or baby birds may be threatened by predators. Additionally, the newly hatched birds
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require relatively small fish because they have small beaks and the adults feed them whole, not regurgitated,
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fish. Concern has been expressed that construction of the project during nesting season could increase
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turbidity in the nearby foraging area, necessitating greater distances for foraging and therefore resulting in
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increased predation while the adults are gone from the nest.
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Figures 4.4-13 through 4.4-17 provide a graphic representation of the relative distance between tern
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nesting locations, which are generally near lagoons and river mouths, and the borrow and receiver sites
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where turbidity would be generated. Distances from the nesting locations are shown in one-quarter, one-
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half, one and two mile increments so the relative location of project features is evident. It should be noted
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that the center point for calculating the distances is the river mouth, as requested by the USFWS, but the
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actual nest locations may be well inland from this point.
For example, a least
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Regional Beach Sand Project EIR/EA
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