7733

• UCREFRP Catalog Number: 7733
• Author: McAda, C. W.
• Title: Evaluation of Aerial-Video Measurement of Backwaters as Part of the Interagency Standardized Monitoring Program for Age-0 Colorado Squawfish.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

1

abundance indices when backwater area was considered. Mean CPE rose and fell with
changes in estimated abundance of small Colorado squawfish in most cases. However, we ,
can not determine whether the estimated number of fish is truly representative of the total
number of fish available. We could calculate confidence intervals for a population estimate, '
but confidence intervals imply more precision than is truly present in the estimates.
Although the number implies information about total number of fish available, it is still only
an index to their relative abundance, just as CPE is. Furthermore, unmeasured changes in '
backwater area (because of changes in streamflow) between video collection and ISMP
sampling will add considerable unmeasured error to any estimate of fish abundance. The '
question then becomes whether aerial video should become part of the monitoring program
simply to supply total surface area of backwaters and allow this calculation. Based on the
cost of the program and the small amount of additional information provided (with its '
unmeasurable potential error), it is difficult to justify aerial video as an annual component of
ISMP. 1
Making other changes in fall monitoring of YOY Colorado squawfish might make more
improvements in the program than were observed by measuring backwater area from aerial ,
video. However, these other additions have negative aspects as well. Simply increasing the
number of seine hauls taken during ISMP will improve the reliability of CPE as an index of ,
relative abundance. However, as pointed out by McAda (1989), increasing the sample size
(number of seine hauls) by 100% only results in a 5 to 20% 'improvement' in abundance
indices (determined by the power to detect significant changes in CPE with appropriate ,
statistical tests). The increased manpower required by the additional sampling effort must be
evaluated when considering changes to the program.
Refining the criteria used to select sampling sites might also improve reliability of fall '
ISMP monitoring. The monitoring program records water temperature and estimates depth
and total surface area in the sampled backwaters, and provides minimum criteria that
backwaters must meet before being sampled. These criteria attempt to reduce variability by '
restricting sampling to habitats more heavily used by YOY Colorado squawfish. Haines and
Tyus (1990) reported that YOY Colorado squawfish in the Green River were most abundant
in backwaters > 15 cm deep, but detected no selection for backwater size (surface area).
They also reported no apparent selection for water temperature in fall. In contrast, Tyus and
Haines (1991) reported a slight (but not significant) preference for larger and warmer '
backwaters. ISMP samples only backwaters with surface area greater than 30 mZ and
maximum depth greater than 30 cm (unless the water is turbid). These restrictions on '
backwater depth and size already consider the limited preferences identified above. Further
analysis of these physical data may help us understand more about habitat preferences of
18